casitas de gila guesthouses bed and breakfast new mexico 575-535-4455

Southwestern Guesthouses on 265 Acres
near Silver City, New Mexico
overlooking Bear Creek and the Gila Wilderness

Casitas de Gila Nature Blog

Casitas de Gila Nature Blog




gila wilderness with snow

El Niño Winter of 2015-16: Fresh snow on the Pinos Altos Range in the Gila Wilderness, five miles north of Casitas de Gila


Historical records show that El Niño winters in the Southwest are marked by increased precipitation and warmer temperatures, while La Niña winters are marked by decreased precipitation and colder temperatures. During El Niño years, moisture-laden low pressure systems coming in off the Pacific Ocean tend to follow a southern route, carried along by the west-to-east flow of a persistent Pacific Jet Stream across the Southwest and into southern New Mexico (see Figure 1 below.) During La Niña years, however, eastward-moving, moisture-laden low pressure systems coming in off the Pacific Ocean tend to take more northerly routes across the western U.S., carried along by the west-to-east variable flows of the Pacific and Polar Jet Streams, bringing dry, sunny high pressure conditions to prevail over the Southwest and New Mexico.

el nino and la nina

FIGURE 1: Schematic drawing showing climatic weather patterns of La Niña and El Niño for North America. Prepared by NOAA/ National Weather Service/ National Centers for Environmental Prediction.


Sea surface temperatures fluctuate constantly in the Central Pacific along the equator, and when monitored and averaged over time demonstrate repeated oscillations between El Niño (warm) and La Niña (cold) episodes. The U.S. National Oceanic and Atmospheric Administration (NOAA) monitors these oscillations by averaging monthly measurements of surface sea water temperatures collected over an area that covers the central portion of the Pacific Ocean between 5°N and 5°S latitude and 120° to 170° W longitude. These temperature fluctuations, when averaged over successive three-month intervals during the year (which NOAA refers to as “seasons”), yield temperature anomalies that NOAA calls the Oceanic Niño Index (ONI). ONI values generally lie within 3°C of the average temperature for any given area at any specific time of the year. Anomalies that deviate from the average temperature in excess of +0.5°C mark a shift towards a warm El Niño episode, whereas anomalies in excess of -0.5°C mark a shift towards a cold La Niña episode. Anomalies that are between ±0.5°C are called a Neutral Episode, or, as they are sometimes humorously referred to, a La Nada episode. By NOAA’s definition, an El Niño or La Niña episode can only be so named when the average of three consecutive ONI three-month seasonal values exceed the ±0.5°C threshold.


When plotted through time as shown in Figure 2 below, it is very clear that El Nino and La Nina episodes are predictably cyclic in nature, with an average duration between 3 and 4 years. Although these episodes do show variability in both duration and intensity, they are not unusual in any way, and are just another of Nature’s cycles that has a pronounced affect upon the natural environment and plant and animal populations in the American Southwest.

el nino and la nina cycles

NOAA graph showing 65 years (1950 to 2015) of El Niño (red) and La Niña (blue) cycles


As can be seen in the Oceanic Niño Index, the American Southwest entered a Neutral or La Nada episode beginning around March of 2012. This La Nada episode continued throughout the rest of 2012, 2013, 2014, and into the first two three-month monitoring periods of 2015. However, beginning in the third three-month interval of February/March/April 2015, the ONI shows a weak El Nino episode gradually strengthening throughout the year to become a very strong El Nino episode by December 2015. Current projections (.pdf file) as of January 4, 2016, have the strong El Niño conditions continuing throughout the rest of the 2015-16 Winter, followed by a slow transition into an ENSO Neutral episode or La Nada situation by Late Spring or Early Summer.


Precipitation at Casitas de Gila has been monitored electronically on a daily basis for many years. Some of this data is presented in Tables 1 and 2 below. Examination of this precipitation data illustrates the transition of a persistent La Nada episode to a strong El Niño episode between March 2012 and December 2015.

As can be seen in Tables 1 and 2, there is a marked increase in precipitation from 2012 to 2015, on a yearly total basis and also when comparing Fall and Winter month totals. The NOAA projection for the Oceanic Niño Index (ONI) for the remainder of the 2015–16 Winter is to remain in an El Niño episode, returning to a Neutral or La Nada episode in Late Spring or Early Summer. If this projection holds true, the Fall and Winter total precipitation should exceed the 2014-15 total precipitation.

rainfall table

rainfall tables


Casitas de Gila is situated on the western edge of Bear Creek Canyon about 80 feet above the Creek overlooking the 265 acres, 3/4 mile of Bear Creek, and 6 miles of trails that constitute the Bear Creek Nature Preserve.

During the time period from March 2012 and December 2015, various changes have been observed in the flora and fauna of the Bear Creek Nature Preserve at Casitas de Gila Guesthouses which may be in response to the transition from the La Nada episode to a very strong El Niño episode as documented in Tables 1 and 2. Some of these observations are presented below. In considering these observations, it must be stressed that they are the result of long-term, daily, on-site personal observations only, and not the conclusions of a rigorous scientific study. It is also important to remember the important principle that must always be kept in mind when dealing with any study of Nature, namely: that “Correlation does not necessarily equate to Causation”. With those caveats stated, the following possible affects of the transition of the La Nada episode of 2012 into the strong El Niño of 2015 are presented:


doubting mariposa

The marvelous Doubting Mariposa Lily (Calochortus ambiguus) found blooming on April 25, 2015, at Casitas de Gila as a result of the 2014-15 El Nino Winter moisture; this is the first time this flower had been observed at the Casitas

• During and in the months immediately following the very dry year of 2012 (total precipitation 6.86 inches), and cold Winter of 2012-13, flowering and seed production of trees, shrubs and grasses at the Casitas were much below normal. Numerous individual plants of several species, such as the Turpentine Bush (Ericameria laricifolia) and Engelmann Prickly Pear (Opuntia engelmannii), on the Casitas’ Self-Guided Nature Trail were observed to die. Spring flowers in particular were notably absent.

• As yearly and Fall/Winter precipitation steadily increased during the transition from La Nada to El Nino, flowering and seed production likewise increased, culminating in the Spring of 2015 when a profusion of flowers occurred over the Casita lands. So profuse and obvious was this prolific flowering of diverse species (some of which had not been seen in many years, and others, such as the Doubting Maricopa Lily (Calochortus ambiguus), had never been observed or recorded previously at the Casitas), that it became the subject of two Nature Blogs in March and April of 2015.


whitewater-baldy fire in gila wilderness

The Whitewater-Baldy Fire on May 22, 2012, 25 miles in the distance as viewed one mile from the Casitas

• 2012 was a year of severe drought and a very difficult time for animals both at Casitas de Gila and at the adjacent Gila National Forest and Gila Wilderness. This was also the year of the Whitewater-Baldy Complex Fire which became the largest forest fire in New Mexico’s recorded history.The fire started on the west side of the Mogollon Mountains just within the Gila Wilderness about 25 miles northwest of Casitas de Gila on May 9, 2012, when two dry-lightening strikes touched off the drought-parched forest. The resulting conflagration was finally declared controlled on July 31, after burning some 297,000 acres of the 600,000 acres of the Gila Wilderness, at an estimated cost of $100 million dollars. This incredibly destructive fire was the subject of a Nature Blog in September 2013.

The combination of the Whitewater-Baldy fire and the ongoing drought of 2012 resulted in some expected and unexpected changes in animal populations and occurrences within the Bear Creek Nature Preserve.

• With the lack of Spring rains in 2012, stock tanks in the mountains adjacent the Bear Creek Nature Preserve dried up early and normal Spring grass and shrub vegetation in the uplands was deficient to completely lacking. Consequently, Bear Creek in front of the Casitas (which always has water in it year around) saw an increase in animals, both large and small, as it was the only source of water and food around. Some of the increase was probably also due to animals fleeing the Whitewater-Baldy Fire in the adjacent Gila Wilderness. Black Bear, Rocky Mountain Bighorn Sheep, and Mountain Lion (the only predator of the Bighorn Sheep) sightings at the Casitas and on Bear Creek were up. Adult Bighorn populations seemed normal; however, only two newborn lambs were observed during 2012 at any one time on the cliffs following lambing in Late Spring. In June a mother Black Bear brought her two cubs to Bear Creek for food and water, and for the first and only time in the 18 years history of the Casitas, garbage cans were raided by the bears.

• In 2013 and 2014, precipitation increased as the overall climate moved towards the El Niño episode. In the early morning hours of September 22, 2014, the largest flash flood ever recorded at Casitas de Gila in its 18-year history occurred when the remnants of a major hurricane in Baja California triggered a series of thunder storms traveling down the Bear Creek drainage from its headwaters in Pinos Altos, creating a flood crest of 12 feet above normal Creek level. The effect of this flood upon less-mobile animals, such as reptiles and amphibians, was undoubtedly devastating, as their observed populations were significantly less in succeeding months.

Most other animals were observed to prosper during 2013 and 2014. During this time the frequency and count of both Bighorn Sheep and Mule Deer sightings increased in 2013, with five Bighorn lambs observed in Late Spring. No Bighorn lambs were observed or recorded in 2014, however.

• In 2015, the El Niño episode arrived with the greatest total yearly rainfall in four years. It was a year of relative plenty in terms of both food and water for all animals, big and small. Bighorn sightings increased with up to 16 individuals observed at one time, 5 of which were lambs. Mule Deer sightings were also up in frequency and count number. Small animals such as Rabbit (both Cottontail and Jackrabbit), Gray Fox, and Field Mice appeared to be much more abundant than in previous years. By the end of the year the Gray Fox population obviously had boomed, based on the amount of scat observed around the Casitas. The chipmunk population, however, was noted as having greatly declined by the end of 2015. Mr. and Mrs. Fox? Most likely.



When all of these various observations are considered together, it is clear that the climatic impact of the La Nada to El Niño transition upon plant and animal populations and the overall food chain during the cyclical transition from the 2012 drought to abundant precipitation in 2015 is definitely mirrored in the observed cycles of plant and animal population and reproduction variability. Some of these cyclical changes are obvious, others only suggested. What is certain, however, is that the overall ecology of the Bear Creek Nature Preserve provides a unique opportunity to observe first-hand the eternal cycles of Nature on a micro-scale for those who have the patience to observe, study and learn.

snow on the Gila Mountains

El Niño Winter of 2015-16. Fresh snow on the Mogollon Range in the Gila Wilderness, 10 miles northwest of the Casitas


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Fall Color in Southwest New Mexico

Color, Light and Shadow Amongst the Floodplain Cottonwoods and Sycamores

fall color in southwest new mexico

Cottonwoods in Peak Fall color on Bear Creek in front of Casitas de Gila, looking north to Turtle Rock and Gila Wilderness beyond

fall color at Casitas de Gila

In like form, about five miles north of the Casitas, within the Upper Box of the Gila River floodplain in the Gila National Forest, golden Cottonwoods arch into a deepening cobalt sky

Bear Creek fall color

On the Bear Creek floodplain below the Casitas, a grove of mature Cottonwoods catch the last rays of the setting Sun

Each year between the last two weeks of October and the first two weeks in November, visitors to Casitas de Gila Guesthouses are treated to the annual visual feast of color, light, and shadow along the floodplains of Bear Creek in front of the Casitas and at the nearby Gila River Riparian Preserve in the Gila National Forest.

fall color along Bear Creek near Silver City

In early morning light a small Velvet Ash in peak color casts long shadows beneath a towering Cottonwood on the Bear Creek floodplain below the Casitas

fall color along Bear Creek near Silver City

Looking down from the Casitas to the Bear Creek floodplain, deepening shadows gradually extinguish the light on the Cottonwoods and Sycamores ablaze in the last rays of the setting Sun

By Late October and Early November, the bright cerulean-blue skies of Summer are in transition to the deeper cobalt blues of Winter as the Sun arcs ever closer to the southern horizon. At this time the deep verdant greens of the dense riverine forest of Cottonwood, Sycamore, Willow, Ash, and Walnut are transformed into an evolving kaleidoscopic display of varying shades and tones of yellow, orange, red, brown, and purple as each of the species responds in its own way to the increasingly colder nighttime rivers of air that flow down into the canyons from the lofty mountain peaks of the Gila Wilderness to the north.

late afternoon light on Bear Creek in New Mexico

Late afternoon on Bear Creek, just upstream from the cliffs, November 11, 2014

early morning light on Bear Creek in New Mexico

Early morning on Bear Creek, just upstream from the cliffs, November 12, 2015

Depending on the year, the time of transition from first coloring to that final blaze of glory for each of the species can be prolonged or remarkably all-too-short depending on the vagaries of temperature, precipitation, wind, and controlling weather systems. This year the change was gradual and prolonged in response to a strong El Niño weather pattern dominating over the southwest, bringing milder temperatures and above-normal precipitation.

fall along the Gila River

Late afternoon in the Upper Box of the Gila River, November 18, 2015; this is the exact same scene as photo on left, but one week later, and what a difference! By this date the leaves of the Cottonwoods and Sycamores are now at their peak

fall along the Gila River in New Mexico

Late afternoon in the Upper Box of the Gila River, November 11, 2015; at this date the Cottonwoods and Sycamores are about halfway to reaching full color

One of the greatest joys of living surrounded by nature at the Casitas is the opportunity to visit and observe the same sites along Bear Creek and the Gila River on a frequent daily basis throughout the year and at different times of the day. Typically, the changes are slow, the change measured in weeks. However, come Fall and the coloring of the leaves, the changes are measured in days, especially towards the end of this month-long process. At this time the rate of change gradually accelerates to literally overnight transformation as Mother Nature completes her annual tapestry in color and signs it with an artistic flourish.

southwest New Mexico fall color

Looking east down the trail leading into Bear Creek Canyon below the Casitas on an early November afternoon; North and South Peak in the background. The white rock at the top of the cliffs directly above the top of the big Cottonwood is a large boulder of welded ash flow tuff, most likely placed there as a way-marker by the Apaches who traveled Bear Creek frequently.

Cottonwoods (Populus fremontii) are typically the dominant floodplain tree along Southwest New Mexico rivers and creeks. When their fall colors are at their peak, Bear Creek Canyon and the nearby Gila River Valley are literally transformed into rivers of gold. Taking a quiet walk within a mature grove of floodplain Cottonwoods on a warm afternoon at this time of year is to experience the essence of the Old Southwest, of times long ago when most of these river and creek valleys served as the primary trails and early roadways for the peoples of the Prehistoric and Pioneer Southwest. To pause and sit beneath one of these ancient Cottonwoods in the pervading silence will only heighten the experience … listen to the wind rustling high above in the upper branches; watch as the golden leaves spiral down to coat the canyon floor, their trunks reflecting in the still waters of the creek. Remain there for a longer time and perhaps the snapping of twigs will herald the approach of a trio of young Mule Deer, or possibly a furtive Bobcat on its way for a drink at the creek …

fall color in southwest new mexico

Cottonwood trunks reflecting in Bear Creek near the cliffs

cottonwoods and sycamores in fall color

Cottonwoods and Sycamores at the peak of Fall color on the Gila River floodplain in the Upper Box of the Gila; it is said that Watson Mountain in the background was a favorite stronghold of the Apache Chief Geronimo

Be assured that Mangas Coloradas, Geronimo, Victorio, Naiche, and the other Apache chiefs and their people passed where you sit on such an afternoon not all that long ago, for this was their homeland … the heart of Apacheria. And a few hundred years before the Apache, the Mogollon People were harvesting their crops of maize, squash, and beans on the first terrace above the floodplain, perhaps just across the stream from you. It is reported that for some people, their presence is still sensed here.

ancient sycamore on Gila River

A magnificent ancient Sycamore on the Gila River floodplain in the Upper Box of the Gila; it is highly likely that Geronimo passed near this tree on his way upstream to his Watson Mountain stronghold

Once the Cottonwoods pass their peak of color, the Sycamores (Platanus wrightii) then emerge in striking visual accent and counterpoint from the mass of Cottonwood Gold, their russet-red star-shaped leaves and bone-white trunks and limbs set against the cobalt blue sky. For the photographer or landscape painter the sycamores are a special delight, particularly when their reddish leaves and white branches are reflected in the waters of the passing stream.

sycamores along the Gila River

Two young Sycamores in peak Fall foliage on Bear Creek floodplain, November 18, 2015; note the tall Cottonwoods in background with golden leaves only remaining in uppermost branches at 50 to 60 feet, their lower leaves having turned and fallen earlier due to the much colder air flowing down the canyon at floodplain level

sycamore leaves

Large and small Sycamore leaves and a few Willow leaves with a bright green accent of watercress in a quiet pool along Bear Creek

winter sycamore in Southwest New Mexico

Another flood-battered Sycamore in Elliot Canyon off Lower Little Dry Creek; note the height of battering on trunk on right, and the 3+ foot red rhyolite boulder wedged in between trunks. Sycamores are indeed the Warrior Giants of the floodplain forest.

magnificant winter sycamore in New Mexico

A magnificent old and flood-battered Sycamore in Elliot Canyon off Lower Little Dry Creek

On some creeks, such as the lower reaches of Little Dry Creek a few miles upstream from its junction with the San Francisco River, Sycamores are the dominant floodplain tree, replacing most, if not all, of the Cottonwoods. The reason for this change is readily discerned in the gnarled and battered appearance of their trunks and lower branches. For where Sycamores are found to dominate, one quickly observes that these are high gradient, high energy creeks; creeks that are often the scene of raging floods and flash floods that stem from Springtime melting snows and Summer Monsoon thunderstorms in the nearby soaring mountains.

Torrential floods transport large volumes of coarse sediment and gravel. Often they carry boulders as big as small cars that crash into the Sycamores, gouging big holes in their trunks, and occasionally washing or tearing away all of their roots, causing them to fall. But many Sycamores can stand this perennial onslaught of Nature and grow to great size and age. Sycamores are much tougher and harder than Cottonwoods, which, even if by chance were to germinate and start growing here in these rocky canyons during a cycle of years of less severe flooding, would be quickly eliminated when the big floods occur.

Sycamore root with boulders

Closeup of Warrior Giant Sycamore in process of digesting rhyolite boulders!

Frequently, one of these ancient and gnarled Sycamores will be observed growing around and beginning to encapsulate one of these huge flood-carried boulders. Often it appears as if the tree is in the process of digesting the boulder. Oh yes, these deep canyon Sycamores are without a doubt the Warrior Giants of the floodplain forest, and they proudly display their battle scars for all who choose to pass here as proof of their prowess.

Velvet Ash in Southwest New Mexico

A beautiful Velvet Ash in a drywash near the Casitas in full Fall foliage

Along the banks of calmer creeks, such as Bear Creak, a variety of Willows (Salix sp.), Velvet Ash (Fraxinus velutina), and Arizona Walnut (Juglans major) grow to more modest size in comparison to the Cottonwoods and Sycamores. These smaller shrubs and trees present a variety of colors from yellow to orange and red to purple which provide both visual harmony and counterpoint accents to the larger and taller Cottonwoods and Sycamores. These trees almost always color and lose their leaves earlier because of their closeness to the floodplain floor where the cold nighttime air flowing down the canyons is often 10 to 15 degrees colder than the upper branches of the floodplain Cottonwoods and Sycamores.


Gila River floodplain

Where the Ancient Ones Once Tread: Floodplain Cottonwoods in the Upper Box of the Gila

Gila River fall trees

Fall in the Upper Box of the Gila. Looking upstream at the junction of Mogollon Creek and the Gila River; Watson Mountain in the background

Over time, as one becomes familiar with the various segments of a particular creek or river, one eventually will come to recognize some “special places” — unique places where the balance and harmony of Nature’s landscape is perfect in every aspect. These are the uncommon places for which the Naturalist, photographer, or landscape painter blindly seek, but instantly know when encountered — places that cannot be summoned or set up, but, at that moment, just are.

sycamores along the Gila River

Looking downstream, Sycamores in the Upper Box of the Gila River, November 11, 2015

sycamores along Gila River

Looking downstream, Sycamores in the Upper Box of the Gila River, November 18, 2015

Sycamore in fall color along Gila River

Floodplain Sycamore, Upper Box of the Gila River, November 18, 2015

A few of these places have an extended timelessness in which their specialness prevails and can be savored slowly again and again; however, most do not. No, for most of such places, this ineffable specialness is fleeting, often measured in mere minutes as the play of light and shadow transforms the common into a brief perception of the Divine. These are the true treasures of Nature, and in Southwest New Mexico during those few weeks of Fall Enchantment from Late October to Mid November is when they are most likely to be found … and they wait for you here every year.

Fall in the Upper Box of the Gila, New Mexico

A late Fall evening in the Upper Box of the Gila River,­ November 18, 2015

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Red Harvester Ants in Southwest New Mexico


red harvester ants

The largest and oldest Red Harvester Ant Colony at Casitas de Gila; located on the west side of Bear Creek just below the Casitas, midway up the slope between the first and second creek terraces above the floodplain

Hike almost anywhere below 6,000 feet elevation in Southern New Mexico where the ground has a few feet of soil cover, and especially where some grass is present, and you will probably come across circular, barren areas, some up to 30 feet in diameter, that are typically devoid of all or almost all vegetative growth. Upon closer examination, one soon notices that these barren areas all contain a central low mound of clean, well sorted, coarse sand to granular pieces of quartz and rock. Pondering these strange features in the early morning, a cool, cloudy day late in the Fall or early Spring or during the hottest part of a Summer day, it may not be immediately evident what produced them. But stand there long enough and the answer will eventually become suddenly and perhaps painfully clear as the first of them begin to make their way up your pant leg and start to bite and sting! Yes, these ARE ant nests! An ant colony to be correct, home of Pogonomyrmex barbatus, New Mexico’s Red Harvester Ants. And what interesting little creatures they are!

There are 44 genera and over 200 different species of ants in New Mexico, but perhaps none have been studied as much as the Red Harvester Ant. One of the reasons that they have been studied so much is because they are big, about 8 to 10 mm or 3/8ths of an inch! Another is that their colonies make very obvious nests that dot the New Mexico landscape. Larger nests are readily seen on Google Earth’s aerial photos. Several years ago this entomologically-challenged, geology-oriented naturalist found this out after laboriously following his GPS through rugged Mule Creek Country terrain to a number of these puzzling circular features discovered on Google Earth while previewing an upcoming hike.

red harvester ants

Massing of Red Harvester Ants (Pogonomeryx barbatus) warming up on a rock; National Park Service photo

casitas de gila guesthouses

Red Harvester Ant Colony on east side of Bear Creek at Casitas de Gila Guesthouses; this colony has a central mound 9 inches high and 6 feet across encircled by a cleared area14 feet in diameter; colonies such as this are easily seen on Google Earth

It was 18 years ago, when Casitas de Gila Guesthouses were just getting started, that the presence of Red Harvester ants was discovered on the premises. Yes, the hard way, as described in the opening paragraph above! It was soon after that Ants At Work1, a delightful and well-written little book about these fascinating little creatures, came our way. Ants At Work is the result of a 17-year study by Deborah Gordon of 300 colonies of Pogonomyrmex barbatus that were scattered over a 25-acre site in SE Arizona and SW New Mexico. Ms. Gordon began her research in 1985 as a graduate student, continued it as a post-doctoral researcher and later a faculty member at Stanford University.


The facts cited below about Red Harvester Ant colonies are mostly from Deborah Gordon’s book, Ants At Work.

Red Harvester ants live in large underground colonies consisting of a queen and several thousand attending worker ants. Once reaching mature status, at about five years of age, a colony consists of an essentially stable population of about 10-12,000 ants. Each colony has only a single queen who will produce all the ants born in that colony for her entire life and the life of the colony, which commonly lasts for 15 to 20 or more years. When the queen finally dies, the remaining worker ants, whose lifespan is only a year or less, soon die off also, with the result that the entire colony dies, leaving an empty colony nest that is never occupied again.

red and black harvester ants in New Mexico

Photo of a Red Harvester Ant and a Black Harvester Ant in their winged alate form, near Tucson, AZ during Summer Monsoon mating season. Photo by Charles Hedgcock, Charles Hedgcock Photograpy, Tucson, AZ, Wikimedia Commons

Colonies begin to propagate new queens and fertile males, called alates, on an annual basis when a colony reaches about five years of age. At that time a new colony is produced when a single, winged “queen” alate from one parent colony is fertilized by a winged male alate from a different parent colony during the annual Summer Monsoon swarming and mating season. Once mated, the queen flies off to a new location, leaving behind her one-day-stand mating male, who will die within a couple of days, if he is not eaten first by a horned toad, bird, or other insect. Once the mated queen lands, she runs around for a short time before dropping her wings, and now, on the first night after mating, digs a hole some 12 to 18 inches deep, enters the hole and blocks off the entrance, never to emerge above ground for the rest of her lifespan, unless the colony decides to move. Within a few days she lays her first batch of eggs which will hatch within about 6 weeks in the form of tiny, worm-like larvae, which soon turn into pupae, that look like ants enclosed in a papery case. When the ants finally emerge from their pupal case, they do so as full-sized adults that do not grow anymore. Thus, a new colony is born.

red harvester ants in New Mexico

Red Harvester Forager Ant carrying a millet seed to the Studio Colony Nest

Colonies of Red Harvester Ants depend on plant material, primarily in the form of seeds as their main food source, which is sought out and brought back from the areas surrounding the colony by outside-the-nest worker ants, where it processed and stored for winter use by inside-the-nest worker ants. About 25% of the colony works outside during the day; the rest stay inside tending to the nest. Colony worker ants can be divided into four groups based on the type of work they do: Patrollers, Foragers, Nest Maintenance Workers, and Midden Workers. Patrollers determine the area to be harvested each day by scouting the area surrounding the nest for food and marking trails by emitting a chemical scent to these food sources which the Foragers will then carry back to the entrance of the nest. Nest Maintenance Workers pick up the food at the entrance to the nest and carry it down into the nest where it is processed and stored, and also bring up sand from the nest below that is added to the ever-growing mound of coarse sand and granules surrounding the entrance to the nest. Midden Workers work on the surface of the mound surrounding the entrance of the nest sorting and moving refuse, debris, and waste material brought up from inside the nest into trash heaps called midden piles which are generally found at the edge of the mound.

harvester ant mound

Mound of coarse sand and granule-sized rock with two entrance holes

harvester ant colony

Closeup of colony mound entrance with ants with typical coarse sand and granules of rock comprising mound and Red Harvester Ants on cottonwood leaf

Below the external mound of sand and granules lies a cone-shaped nest that tapers downward consisting of a mass of ¼ to ½ inch chambers with curved ceilings and walls connected by tunnels of varying widths. The chambers in the upper part of the nest that connect directly to the nest entrance hold the 25% of the colony that works outside the nest. The lower chambers are dedicated for various uses, some as living chambers for the Nest Maintenance Workers, some as food storage chambers with neatly stacked seeds, others are brood chambers for the young, the larvae carefully laid out on the floor of the chamber, and the solitary chamber holding the queen. The nest extends downward about as deep as the surface mound is wide, about 10 inches for a 2-year old colony and 5 feet for a 6-year-old colony.


Red Harvester Ant colonies can be found over most of the land around the Casitas. The largest colonies and oldest colonies, however, are found in Bear Creek Canyon, scattered at intervals over and along the first and second terraces above the floodplain, where vegetation tends to be more abundant and dependable from year to year than on the hillsides or on the flats surrounding the Casitas. Below is a photo essay of representative Red Harvester colonies from the largest and oldest to smaller and younger colonies at the Casitas.

The Largest and Oldest Colony at the Casitas

large red harvester ant colony

Largest and oldest Red Harvester Ant Colony at Casitas de Gila Guesthouses, designated L7-3 on Casitas Self-guided Nature Trail; mound is 19 inches high, 9-10 feet in diameter at base and is surrounded by 30 foot diameter cleared area; the colony is at least 20 years old

By far the largest and oldest Red Harvester Ant colony at the Casitas is a colony located just below the Casitas on the west side of Bear Creek, with the center of the mound lying about 11 feet above normal creek level, midway up the slope between the first and second creek terraces above the floodplain. The central mound of the nest is cone shaped, measuring 9–10 feet in diameter and about 19 inches in height. The mound is composed of well-sorted coarse sand to granule size particles of sand and rock averaging .11 inches in diameter, which is typical of colony mounds throughout the Casita property. Surrounding the mound is a ring of bare ground, cleared of all vegetation, the outer edge of which measures 30 feet in diameter.

harvester ant colony

Photo of largest and oldest colony taken July 9, 2001

harvester ant colony

Same view of largest and oldest colony taken November 5, 2015; note 60-ft. cottonwood trees in background not present in 2001 photo

Age of this monumental colony is at least 20 years, and it is still active. The colony was first observed when we bought our land 18 years ago, and although measurements of its size were not made at the time, it was considered the largest colony mound observed on the property. Because of its impressive size, it was designated as Stop L7-3 when the Casitas de Gila Self-Guided Nature Trail was established in July 2001. As shown in a photo taken at that time, the size of the mound is estimated to be at least 5 tor 6 feet in diameter which, based on Gordon’s research, would suggest an age of at least 6 years.

During the 12-foot flash flood of September 22, 2014, Bear Creek came up to the lower edge of the mound.

Second Oldest Colony at the Casitas

bear creek new mexico

Photo of second largest and oldest colony located on east side of Bear Creek across from the Casitas and built on floodplain; colony was submerged under 4 to 5 feet of water and mound washed away during September 22, 2014 flood

Downstream, and on the opposite (east) side of the Creek from the Oldest Colony, is the Second Oldest colony known on the property. This colony is interesting because, based on its size, it was established on the floodplain itself about 10 years ago about 7 or 8 feet above the creek, following the Great Flood of February 2005, when Bear Creek switched from the east to the west side of Bear Creek Canyon in front of the Casitas. During the 12-foot flash flood of September 22, 2014, this mound was submerged for several hours beneath 4 or 5 feet of rushing water which washed away all of the central mound. The colony survived, however, as most ants can survive underwater for 24 hours or more, and as the October 2015 photos show, was well on its way to rebuilding the central mound.

A Middle Aged Colony at the Casitas

harvester ant colony

Photo of middle-aged colony with 6 foot diameter mound and 14 foot diameter cleared area

Near the north end of the Willow Walnut Trail, on the west side of Bear Creek, lying about 13 feet above creek level, a typical middle-aged colony is found on a wide, old, creek terrace surrounded by grass and mesquite. The cleared area around the central low mound is about 14 feet in diameter and the central mound is about 6 feet in diameter and 8 inches high. This colony would be at least 6 years old.

A Young Colony at the Casitas

young harvester ant colony

Photo of young colony; note almost lack of mound and cleared area

A few yards south of the middle-aged colony a young colony is found. Lacking a peripheral cleared area and an obvious central mound, only the concentrated deposits of the telltale coarse sand and granule sand and rock material surrounding the inconspicuous entrance to the nest identify this as a Red Harvester Ant Nest. Age of this colony is less than 5 years, perhaps 2 or 3 years old.

Encountered away from the nest, Red Harvester Ants are not aggressive and will rarely attack or bite the strolling or resting hiker, but will simply carry on with their perceived personal mission, whatever that may be. However, for the preoccupied hiker or obliviously engaged birder who unwittingly pauses within their cleared area, or near the entrance of a not-so-obvious young colony such as this one, for more than about 30 seconds, it will be, shall we say, a most memorable learning experience. Soon, those open pant legs will become the center of attraction for a host of the colony’s Patrollers, Nest Maintenance, and Midden Workers who will do their collective best to remove you from their premises! The actual bite of the Red Harvester ant itself may or not be all that painful, sometimes going unnoticed . . . for awhile . . . but after a few hours will eventually produce a large welt from the venom it has injected in the various parts of one’s lower anatomy. Depending on one’s own chemistry and allergic reaction, these welts can be either itchy or burningly painful . . . or both. But eventually, like maybe in three to five days (as is the case with this humble naturalist), they will suddenly disappear. Taking good hot showers seems to speed the process of recovery and during the interim of healing will act both as a temporary palliative on the welts as well as a provider of rather unusual exotic sensations!


Here at Casitas de Gila we have been feeding the wild birds between 50 to100 pounds of birdseed a month, year-around, for some 18 years now, for the enjoyment of our guests as well as ourselves. Behind the office and our Casa we have established a feeding station where we sit each morning having a cup of tea while discussing our tasks for the day, and watching what we have come to call the Casa Birds just outside the window. For both of us, watching the comings, goings, and annual return of the wide variety of species that change through the seasons here has become a morning ritual of never-ending pleasure.

feeding birds at Casitas de Gila Silver City

Bird Feeding Station at Casa

young harvester ant colony

One or two year old Studio Colony in foreground, Casa Studio on left. Looking north towards Bird Feeding Station at Casa (hidden behind juniper) with Turtle Rock in background

About 70 feet to the west of the Casa Bird Feeding Station is the Studio, where occasionally we find time to engage in some creativity. One morning this summer, while looking across the canyon to see if the Bighorn Sheep were on the cliffs, a progression of Red Harvester Ants was observed marching along double file in what appeared to be a well-established trail in front of the Studio door, with some ants heading south away from the Studio, and others heading north towards the Casa. Many of the ants heading south appeared to be carrying something in their mandibles, while all of the ants heading north carried nothing. Ah-hah! A Red Harvester Foraging Trail! Where does it go? Following the trail to the south about 40 feet, the nest was soon encountered. It was obviously the nest of a young colony as indicated by the lack of a distinct mound and only the familiar heavy scatter of coarse sand and granule-sized particles of rock to mark the entrance to the nest.

After spending some time photographing the colony’s nest, as well as some of the Foragers that were returning with pieces or whole seeds of some sort, it seemed appropriate to follow the foraging trail northward to possibly discover the source of the food the ants were carrying. Following the trail past the Studio there were places where the ants had literally worn a path 1 to 2 inches wide through the rocks, weeds, dead juniper twigs and grass covering the ground. Eventually the trail ended . . . surprise, surprise . . . at the Casa Bird Feeding Station, or perhaps now more appropriately named, the Casa Bird and Ant Feeding Station. How long this had been going on is not known, but the age of the colony nest is probably only one or two years.

Watching the ants select their next forage seed at the feeding station was interesting. Their criteria for selection was not obvious by any means. Occasionally two ants would spy the same seed at the same time and they would battle over it and around it for a minute or two, like lilliputian wrestlers, before staggering away, both of them leaving the seed behind. Millet seeds and small pieces of cracked corn seemed to be preferred.

ants foraging

Two Studio Foragers on the foraging trail between the Casa Bird Feeding Station and the Studio Colony; the Forager below is heading to the Studio Colony carrying a millet seed; the Forager above is heading to the Casa Bird Feeding Station to pick up more food

ants foraging

“It’s mine! No, I found it first.” Two Forager Ants fighting over a millet seed before both of them go off in different directions leaving it behind


(Note: this section has been written for Children and Eternally Young Naturalists everywhere. The events are true and were observed and documented exactly as reported here.)

After watching this foraging frenzy of the Red Harvester Ants at the Casa Bird Feeding Station for a while, the Humble Naturalist decided to trace the foraging trail back to the Studio. About half way back, a lone Forager Ant was spotted carrying a very different, and seemingly much heavier, load than the other Foragers. It was carrying a whole Sunflower seed. Now the adult Red Harvester Foraging Ant averages about 9 mm (1/3 inch), but the seed that this ant was carrying was longer than it was, measuring 10.4 mm (4/10 inch) long. The measured weight of an average Sunflower seed in the wild bird seed is 0.3g (0.01oz), whereas the average weight of a Red Harvester worker ant is 5.5 mg (.0002oz)2. Thus, this lone Forager Ant was transporting a seed roughly 50x its own weight. In comparison with humans, this would be the equivalent of a 160 lb human transporting 8,000 lbs or 4 tons of sunflower seeds. Now the distance from the Casa Bird Feeding Station to the entrance of the Studio Colony Nest is 110 feet. Since a 6-foot human is 1800 mm and the length of an average Red Harvester Ant is 9 mm, the human is roughly 200x longer than the ant. Thus, to equal the 110 feet traveled by the ant, the human would have to transport that 4 tons of sunflower seed some 22,000 feet or 4.2 miles.

harvester ants

Forager Ant pushing its Sunflower seed along the trail to the Studio Colony

At first the Humble Naturalist thought that the Forager Ant was actually carrying the Sunflower seed along the trail. However, a lengthy series of close-up photos documenting its journey back to the Studio Colony Nest showed that for the most part not only was it pushing the seed along the ground, but it was using appropriate physical engineering principles in doing so. Sunflower seeds have a distinctive shape, namely that of a flattened tear drop, with a slightly bulbous, rounded blunt end and a sharper, more pointy, thinner end, with a pronounced raised rim around the flattened edges of the seed. As the photos show, the Forager Ant for most of the journey did not carry the seed but rather pushed it along the ground by first grasping the narrow axis of the blunt end with its mandibles to stand the seed vertically on the rim surrounding its edge, and then, with the upturned pointy end facing forward much like single runner on a skate, shoving the seed down the trail. By pushing the seed in this manner, and tilting it from side to side, Forager Ant was able to steer the seed over, around, and through the never-ending obstacles of pebbles, twigs, and vegetative material along the trail. Occasionally, when encountering a big pebble or twig, it would switch to the other end of the seed, and grasping the pointy end, drag it over the obstacle, and then resume pushing from the rear. After analyzing numerous photos of Forager Ant’s homeward journey, it was obvious that this Forager Ant had been an honors student in Physics 101 at the Red Harvester Ant Foraging School.

harvester ants

When the going gets tough, a tough Forager keeps going . . .

harvester ants

Despite all obstacles, Forager Ant just keeps pushing . . .

harvester ants

Upon reaching the edge of the colony nest, Forger Ant switches ends on the Sunflower seed to cross the coarse sand and granules thrown out by the Nest Maintenance Workers

Repeated measurement of Forger Ants carrying a single piece of millet or corn from the Casa Bird Feeding Station to the entrance to the Studio Colony Nest gave consistent speeds of roughly 10 feet per minute, or 0.11miles/hour, completing their journey in about 11 minutes. The speed of the Forager pushing the Sunflower seed was not measured at the time, nor was the act of a Forager Ant bringing home a whole Sunflower seed ever seen repeated, but obviously Forager Ant had been moving much slower, perhaps 1/3 or 1/4 the speed of the millet-carrying Foragers, thus taking between 30 to 45 minutes from Bird Feeding Station to Studio Colony entrance.

Eventually, however, after a rather tortuous, physically challenging journey on the trail, Forager Ant reached the Studio Colony Nest. Now, with a impressive final show of strength and speed, Forager Ant attempts to deposit the Sunflower seed right at entrance to the nest, where it is immediately thwarted by an alert Nest Maintenance Worker Ant who grabs ahold of the Sunflower seed and apparently tells Forager Ant, “Not so fast, Forager, that seed is way too big to fit down the hole. Take it away.”

harvester ants

Now, finally at the entrance to the nest, Forager attempts to deposit the Sunflower seed; however, it is met by an alert Nest Maintenance Worker who grabs ahold of the seed and tells Forager that the seed is too big and must be taken away

harvester ants

Dejected at having been turned away after such a long and arduous journey, Forger pushes the Sunflower seed away from the entrance

Dejected beyond belief that its beyond-the-call-of-duty, extreme foraging effort is not appreciated, Forager Ant drags the sunflower seed a short distance away, stops, pauses for a few seconds, and then turns and makes a second attempt at taking it to the nest entrance. Again, and in no uncertain terms, Forager Ant is stopped by the ever-alert Nest Maintenance Ant and told once more to take the seed away. With dejection now having turned to hardly concealed anger, Forager Ant starts to haul the Sunflower seed away, but instead, overcome with rage, throws it against a big pebble, and stalks away in a totally uncharacteristic and unheard of state of rebellious, non-collective Red Harvester Ant Colony Consciousness, emitting faint ant obscenities and obnoxious pheromones as it disappears into the weeds.

harvester ants

Unwilling to give up without a fight, Forager turns and pushes the Sunflower back to the nest entrance, approaching from a new direction

harvester ants

Once again Forager Ant is stopped by the Nest Maintenance Worker before he can deposit his seed at the nest entrance and is instructed to take it away; enraged Forager Ant throws the Sunflower seed against a rock and stalks away


The abandoned Sunflower seed was patiently observed by the Humble Naturalist for quite some time to see what would happen next, and although a few ants came and smelled it, they made no attempt to move it. Returning to the nest an hour or so later, it was discovered that the Sunflower seed had been removed from the rock were Forager Ant had thrown it. What happened to the Sunflower seed is unknown. Most likely is that the Nest Maintenance Worker Ant instructed a Midden Worker Ant to take it to the Midden Pile off to the side of the Mound, but, despite a short search, it couldn’t be found. As to Forager Ant? Also impossible to say, but it is highly likely that soon after the disruptive event, a parable about a radical, Overachieving Forager Ant who brought back food too big to fit through the entrance of the nest would become part of the colony’s teaching curriculum for schooling young ants after they emerged from their pupae in the brood chambers for many years to come.




  1. Deborah Gordon, 1999, Ants at Work, The Free Press, Simon and Schuster, 182 pp.
  2. Robert A. Johnson, 2002, Semi-claustral colony founding in the Seed-harvester ant Pogonomyrmex californicus: a comparative analysis of colony founding strategies, Oecologia, 132:60-67. Springer-Verlag.

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The Gila Cliff Dwellings National Monument

Many Questions, A Few Clues, Emerging Answers

Part 2 of 2

gila cliff dwellings new mexico

We Are Chacoan

The Gila Cliff Dwellings National Monument, located 45 miles north of Silver City in the middle of the Gila Wilderness, is a unique cultural site in Southern New Mexico. Yet, despite 131 years of study and research since the great anthropologist Adolph Bandelier visited the Cliff Dwellings and the nearby TJ Ruins in 1884, and the subsequent discovery of many important clues as to its origin and abandonment, the site is still little understood, its mystery securely wrapped in the silent stones.

gila cliff dwellings silver city

Drawings of Gila Cliff Dwellings made in 1885 during visit by Adolph Bandelier and Lieutenant G. H. Sands. Note T-shaped door. Fig. 11 In Gila Cliff Dwellings National Monument by P. Russell, 1992, Southwest Cultural Resources Center Professional Papers No. 48.

Part 1 of this Blog presents many of the significant facts and data surrounding the Cliff Dwellings and TJ Ruins that have been discovered over the years, along with key questions that the data raise, plus some partial answers and a few speculations. As previously noted in Part 1, it is unlikely that significantly more data will be recovered from the Cliff Dwellings as they are at this time almost completely excavated at the professional level, with much critical information forever lost to looting and vandalism in the years prior to the establishment of the Gila Cliff Dwellings National Monument. The TJ Ruins, however, remain essentially untouched and un-excavated. Whenever the TJ Ruins are excavated, it is considered quite likely to this writer that more answers will be forthcoming to the questions raised in Part 1 of this Blog regarding the Cliff Dwellings, which are repeated below:

  • Who were these Cliff Dwellers anyway and what were they like?
  • Where did they come from?
  • Why did they come, and why did they choose to stay in dark, cold caves as opposed to the large TJ Ruin?
  • Were there people living in at the TJ Ruin site at the time, and if so what was their relationship with the Cliff Dwellers?
  • Why did they stay such a short time? (as suggested by lack of adult burials, lack of trash, lack of building modifications and additions), and Why did they leave?
  • Where did they go?

Until the excavation of the TJ Ruins takes place, there is little more that can be learned directly from the Gila Cliff Dwellings National Monument itself. There is, however, a vast wealth of existing regional Southwest archaeological data and information for what was happening in the Northwest New Mexico portion of the Four Corners Area involving the Anasazi, Chaco and Aztec Cultures from the 10th to the late 13th Century. This data and information, when considered in context with the Gila Cliff Dwellings, offers tantalizing clues and possible answers to the above questions.

Part 2 of this Blog begins with a brief summary of the Rise and Fall of the Anasazi Chaco and Aztec Culture, and uses it to develop a speculative scenario as to the possible origin and abandonment of this mysterious, isolated cultural site of the Gila Cliff Dwellings in Southern New Mexico.


Note: Unless otherwise indicated, most of the facts, data, and information reported in this section
are derived from Lekson, S.A., 2015, The Chaco Meridian1


First Came Chaco . . .

pueblo bonito new mexico

North Wall of Pueblo Bonito (National Park Service historic photo)

Between 850 and 1275 AD, the Four Corners area of the United States (Utah/Colorado/New Mexico/Arizona) witnessed the development of the largest and most advanced Native American culture in the Southwest. This was the Anasazi or Ancestral Pueblo Culture which at its peak between the late 11th and early 12th centuries grew to a population that Lekson believes was “something under 100,000 people”, spreading out as much as 250 kilometers (155 miles) from its geographic, cultural, and political center at Pueblo Bonito in Chaco Canyon. Pueblo Bonito is just one of 12 major Anasazi Pueblo Ruins in the Chaco Culture National Historical Park, which is located in the northwest corner of New Mexico about 100 miles northwest of Albuquerque.

The numerous Pueblo ruins in Chaco Canyon and the surrounding area have been the focus of extensive and still-ongoing formal archaeological research since 1896. In 1907, President Theodore Roosevelt set aside a portion of Chaco Canyon as a National Monument. Additional lands were added over the years. In December 1980, the small National Monument became the Chaco Culture National Historical Park to protect the more than 2,400 archaeological sites within the Park’s boundaries.

chaco culture new mexico

NPS Map of Chaco Culture National Historical Park showing location of major Great Houses

Pueblo Bonita ruin

Looking East from cliff across Pueblo Bonito. Note Great Houses, Great Kivas, and Plaza with Chaco Wash Arroyo in middle distance (National Park Service photo)

After more than a hundred years of archaeological investigations, it is clear that the so-called “Chaco Phenomenon”, a term coined by archaeologist Cynthia Irwin-Williams in 1972, was indeed just that. What took place there was unique in Southwest U.S. archaeology in every sense of the word: from its magnificent and massive 4- to 5-story exquisite stone buildings known as Great Houses, and huge, above and below ground circular-shaped Great Kivas adjoining large adjacent open plazas, to the nearby scattering of small, one-story, single-family Unit Pueblos with a small kiva, to an extensive road system leading to many of the 150 identified surrounding smaller “Outlier” villages as much as a 100 miles or more away, each with their own Great House and Great Kiva and surrounding smaller Unit Pueblos. Indeed, there was nothing like it either before or after what has been collectively referred to as the Chaco World or the Chaco System.

Chetro Ketl New Mexico

Looking Southeast across Chaco Wash Canyon from overlook. Chetro Ketl Great House in foreground. Note multi-story walls and Great Kivas (National Park Service photo)

chaco canyon new mexico

Looking South at Pueblo del Arroyo (National Park Service photo)

In the past two decades, somewhat of a consensus has been emerging regarding a basic understanding of the architecture, social, religious, economic, and political components of the Chaco World. Key aspects of this understanding that are considered important relative to answering the questions posed above regarding the Gila Cliff Dwellings are given below.


pueblo bonito great house new mexico

Multi-story wall of Pueblo Bonito Great House. Note fine stone masonry, roof vigas in wall, and door in corner (National Park Service photo)

Casa Rinconada

Great Kiva at Casa Rinconada. Note T-shaped door in wall on left (National Park Service photo)

In Chaco, named for its location in Chaco Canyon, architecture was of two main types: 1) massive and magnificent Great Houses soaring up to 5 stories high, built of finely worked, thick stone masonry with unique T-shaped doors for all to see, with adjacent, equally large and impressive Great Kivas, bordering large open plazas; and 2) nearby scattered single family, small, 5 or 6 room Unit Pueblos of rough stone masonry and mud, commonly with an adjacent small kiva.

Architecture in the Outlier villages was very similar to that of the major Chaco sites located in Chaco Wash except on a smaller scale: a Great House and Great Kiva with nearby scattered single-family Unit Pueblos.


Chaco Shell Bracelet

Chaco Shell Bracelet, 1050-1100 AD; Shell, Glycymeris gigantean, is from Baja California Sur/Gulf of California Chaco Culture (National Historical Park Museum photo)

Chaco turquoise beads

Chaco Turquoise Beads, 1050-1100 AD, Chaco Culture (National Historical Park Museum photo)

Chaco copper bell

Chaco Copper Bell with Tinkler, from Great House at Pueblo Alto, 1020-1240 AD; loop molded separately and later fused to body. Tinkler (clapper) is made of either stone or clay. These copper bells came as trade goods from Mexico. (Chaco Culture National Historical Park Museum photo)

Chaco culture was stratified, with a very distinct class structure. Chaco was not an egalitarian commune, as was thought by many early on. There were Nobles, Elites, or Lords who lived in the Great Houses and did important things and thinking in the Great Houses; and then there were the Commoners, peons or serfs who lived in the small unit pueblos and labored to build the great buildings and roads, to serve the Nobles, and to toil endlessly in the fields to produce the food for the Chaco system.

The Nobles did no manual labor, nor did they build the Great Houses. The lack of hearths in the Great Houses suggests they didn’t do their own cooking either; food was probably prepared for them by servants or slaves in the plazas where large cooking pits have been excavated.

It was easy to tell the Nobles: they wore exotic jewelry of marine shells and Scarlet Macaw feathers – lots of feathers – and copper bells imported from Mexico, plus turquoise jewelry from Chacoan mines near Outlier villages to the east. And while they sat in the splendor of their Great Houses, talking to their Scarlet Macaws, they drank Cacao (chocolate), also imported from Mexico, from unique and exclusively-Noble cylinder-shaped pottery mugs. and laid plans for their next building or road project. Another important annual decision involved deciding which of the outlier villages that did not get enough rain for their crops that year, but had remained faithful to the Chacoan Code of Rules, deserved to be issued grain from the Chaco Great House storage bins.

The commoners, on the other hand, were typical of all commoners throughout history: born to a lifetime of work from dawn to dark, or born to serve, and if they worked and served well, and above all obeyed the Nobles’ rules, possibly they, too, could acquire a bauble of marine shell or a piece of turquoise, but, except for the extremely good, probably not a macaw feather.




Quetzalcoatl in feathered serpent form as depicted in Codex Telleriano-Remensis (16th Century)

Xipe Totec

Illustration of Aztec god, Xipe Totec as shown in Codex Borgia

Christy Turner2 in his 1999 book Man Corn, Cannibalism and Violence in the Prehistoric American Southwest writes extensively about archaeological and ethnographic evidence that the Chaco World and other Southwestern Native American cultures “received, imported, adopted or adapted elements of Mexican Indian religion or cosmology”. This evidence is seen in rock art (petroglyphs and pictographs), scenes on Mimbres pottery, paintings on kiva walls, and religious paraphernalia and practices, especially those that bear resemblance to two ancient Mesoamerican deities, Quetzalcoatl, the Feathered Serpent and Xipe Totec, “Our Lord the Flayed One”, both of which are associated with ritual sacrifice.



Most archaeologists in working on the nature of Chacoan and other prehistoric Southwestern economies have focused on localized subsistence economies, those based on food (maize, squash, and beans), pottery, rocks (obsidian for projectile points) or human labor. Exotic objects found in Chacoan ruins, such as Scarlet Macaw feathers and skeletal material, marine sea shell jewelry, copper bells, and turquoise, generally received little attention or mention, being considered nothing more than trinkets for “would-be Elites”.

There was a subsistence economy in the Chacoan World, an economy that basically functioned within a 150 km (90 miles) radius of the Chaco Center in Chaco Canyon, where Chaco served as central warehouse and redistribution center to outlier villages, which functioned, perhaps, in some form of a “from each according to their ability, to each according to their need”, or maybe “render unto Caeser the things that are Caeser’s … or else” basis.

There was also, however, what Lekson (2015) calls a “political-prestige economy” which was based on exotic materials and objects such as macaw birds and feathers, marine shell objects, copper bells, jet frogs, cacao, and turquoise. Most of these materials and objects were wearable or easily portable symbols of nobility, office, rank, wealth, and most importantly, Power. This prestige economy could be used in establishing alliances, and extending the Chacoan policy outward to great distances, distances as much as 250 km (150 miles), which lay far beyond the practicalities and logistics of subsistence economies.



While many earlier archaeologists spoke in their own terms of a political hierarchical/class structured society at Chaco, it was not until Lekson (2015) was introduced to the concept of the Postclassic Mesoamerican Altepetl that he felt he had found a political/social/governing system that closely fit the diverse data gathered from over a hundred years of research and excavation of Chaco. As Lekson describes: the altepetl (plural altepeme) consisted of a ruling class of several (6 or 8) ruling families and their associated commoners within a defined agricultural territory. There could be a hierarchy of altepemes with Major Nobles and their Commoners and Secondary Nobles with their Commoners. In this system the Commoners were obligated to contribute a certain amount of goods (crop harvest for example) or labor (building the Great Houses were the Nobles resided) to their Noble families. Major Nobles would live in a larger, centralized or “urban” altepetl such as the magnificent Great House centers of Chaco Canyon, while their Commoners lived in nearby Unit Pueblos. Secondary Nobles would rule over smaller altepemes in the surrounding countryside, the so-called Chaco “Outliers”, living in smaller Great Houses, which would be surrounded by a number of Unit Pueblos where the Commoners lived. In this system, just as Commoners paid tribute in goods or labor to their Noble families, Secondary Nobles were obligated to pay tribute in goods or services to the Major Nobles. While there was a Chief Noble or King, the kingship did not pass down by blood heritage when replacement was needed, but rather the successor was decided upon by the half dozen or so Major Noble families, and generally not chosen from the outgoing Noble family.


Then Came Aztec . . .

Chaco began somewhere around 850 AD and experienced a golden age period of infrastructure and population growth between 1020 and 1125, when construction of buildings ceased. Around 1080 something triggered a decision to move the capital from Chaco Canyon to some 90 km (54 miles) north to what is now known as Aztec Ruins National Momument on the Animas River. The Aztec Ruins are in many ways very similar in architecture and layout to Chaco Ruins with Great Houses, Great Kivas, surrounding complexes of unit Pueblos, as well as some new building designs of circular tri-walled structures. Construction began at Aztec around 1100, about the same time as the building of the Great North Road commenced that would connect Chaco to Aztec, and by 1125, the new capital or center was essentially completed. Aztec functioned as the central seat of power in the Chacoan World until 1275, when a final collapse and abandonment of the Chacoan World took place.

aztec ruins new mexico

Aztec Ruins in the Fall

aztec ruins new mexico

Aztec Ruins with Great Kiva (National Park Service photo)


As stated in Part 1 of this blog, the last part of the 150 year time period, between 1150 and 1300 has long been considered a time period critical to the understanding of two of the greatest mysteries in the archaeology of the Southwest. These mysteries, sometimes referred to as The Great Collapse or The Great Abandonment, concern the time period when two of the three largest and most evolved Southwestern Native American Cultures, the Mogollon and the Ancestral Pueblo (Anasazi), experienced major change and societal upheaval. This upheaval was both widespread, long-term, and chronic throughout their domains, ultimately resulting in the eventual collapse of these two advanced cultures’ social structure, and the subsequent abandonment of their villages and larger population centers. The cause (or causes) of this collapse and abandonment has been the subject of strong and often vitriolic ongoing debate for decades.

Early on in the research of the Chocoan World, archaeologists began to consider chronic drought with accompanying starvation as the primary cause for the collapse and abandonment. In recent years other possible causes have been proposed, such as introduction of new religious beliefs, depletion of resources such as deforestation and subsequent erosion of agricultural lands, and possible warfare or rebellion.

The following sections will discuss several lines of recent research which, when combined, offer strong evidence for a proposed climatic root cause and a resulting political/societal upheaval scenario that led to the collapse and abandonment of the Chaco World. Following that, the proposed scenario will be used to suggest further answers to the key questions raised in Part 1 of this blog about the Gila Cliff Dwellings. We begin with a close look at climate data for the past 2,000 years in New Mexico.


For several years now, as any follower of contemporary news has noticed, there has been a lot of concern over Climate Change and what it means to current civilization. For any student of earth history, Climate Change is nothing new. The Earth’s Climate (as well as its geology, geography, and resident life) has always been in a state of dynamic change, and it always will be. In this section we will take a quick look at the last 2,000 years of Climate Change in New Mexico and its affect upon its prehistoric cultures.

Climate, as defined by Merriam-Webster, and as used here, refers to “the average course or condition of the weather at a place usually over a period of years as exhibited by temperature, wind velocity, and precipitation.” Paleoclimatology is the study of climate change in prehistoric times. Measurement of temperature, and precipitation in the prehistoric past can be determined by a variety of climate proxies. Proxies for ancient wind patterns also exist, but are much less precise; for example, study of a down-wind deposit of volcanic ash from a known or suspected volcanic eruption.


Figure 1 below is a graph from F.C. Ljungqvist’s 20103 reconstruction of global temperature for the last 2000 years in the Northern Hemisphere. The study is based on 30 temperature sensitive proxies, including: historical documents, marine sediment records, lake sediment records, ice core oxygen isotope records, varved sediment records, and tree ring records globally distributed around the Northern Hemisphere between 30° and 90°N.

Ljungqvist’s research has yielded substantial evidence that the changes in global temperature shown by the graph in Figure 1 during the Medieval Warm Period and the Little Ice Age were experienced throughout all portions of the Northern Hemisphere. Figure1 illustrates how these periods of major climate change can be used to better understand major human cultural endeavors in the historic past. Superimposed on Ljungqvist’s graph are historically documented dates for the Viking colonization and later abandonment of Greenland as recorded in the ancient Viking Sagas, as well as in Icelandic writings at that time. As shown in the graph, and confirmed by the historical records and modern archaeological excavations, we can see how climate controlled the Viking colonization and prosperity during the Medieval Warm Period and subsequent abandonment during the ensuing Little Ice Age.

Also shown on the graph are the dates given by Lekson (2015) for the rise and decline of Chaco and the rise and fall of Aztec. It can be seen that the rise of Chaco around 850 and its subsequent golden age coincided with the warmest part of the Medieval Warm Period, and that the climate entered a substantial cooling period around 1080 a few years before construction stopped at Chaco in 1125. The moving of the Chacoan capital from Chaco Canyon to Aztec began during this time period with construction beginning at Aztec around 1110. The building of Aztec took place rapidly so that by 1125 Aztec was flourishing while Chaco was beginning its decline. From 1100 temperature remained fairly stable globally until about 1250 when cooling increased, gradually bringing the Medieval Warm Period to an end and ushering in the Little Ice Age at 1300. During this period Aztec falls around 1275, bringing to an end the Chaco Phenomenon in the Four Corners area.

temperature graph

Fig. 1: Graph of Global extra-tropical Northern hemisphere (30-90°) decadal mean temperature variations (dark grey line), with 2 standard deviation error bars (light grey shading) after Ljungqvist, 2010. Time periods shown for the Roman Warm Period, Dark Age Cold Period, Medieval Warm Period and the Little Ice Age are Ljungqvist’s. Anasazi Chaco and Aztec Culture dates are from Lekson, 2015; Vikings dates are from D’Andrea and Huang, 2011.



lava bridge in El Malpais

Lava bridge with stunted Ponderosa Pine and Douglas Fir in El Malpais National Monument (National Park Service Photo)

When considering the paleoclimate for any area, temperature, of course, is only part of the equation, the other major determinant being precipitation. Fortunately, a very detailed record for precipitation at the time of the Chaco Phenomenon is available for Northern New Mexico from the field of dendroclimatology. Dendroclimatology is the scientific method that uses measurements and patterns of tree rings (also known as growth rings) as a proxy to reconstruct past climate. In 1996, an in-depth research study based on tree ring analysis was published which details past precipitation for the El Malpais National Monument Volcanic Field in Central New Mexico for the last 2,200 years. The Malpais is located only 80 miles south of Chaco Canyon.

Figure 2 below is a graph showing above and below average precipitation for the Malpais National Monument volcanic field lava flow area in New Mexico between 0 and 1650. This graph is based on H.D. Grissino-Mayer’s 1996 in-depth study4 of tree-ring width analyses from 248 measurement series of cores obtained from living trees and sub-fossil wood (dead, down and not decayed) from long-lived Douglas Fir and Ponderosa Pine found in the Malpais. Because of the unique hydrologic conditions in the Malpais lava flow fields, trees growing on the lava flow over the past 2,000 years exhibit a very accurate dendrochronologic record of variations in annual precipitation patterns.

temperature chart

Fig. 2: This graph of annual rainfall in Malpais region New Mexico. Curve is a 10-year smoothed curve of yearly tree-ring width fit to accentuate short-term (less than 50 yr) climate episodes. Horizontal 0 line separates above normal precipitation (Positive standard deviation) from below normal precipitation (Negative standard deviation). After Grissino-Mayer, H.D., 1996. Rise and fall dates of the Anasazi Chaco and Aztec Cultures and drought dates are from Lekson, 2015.

Periods of cyclical drought are an inherent and a defining characteristic of the American Southwest from prehistoric times to the modern present, and can be expected into the foreseeable future. Every culture who has lived there, from the prehistoric past right up to the present, has experienced droughts and dealt with them, with various degrees of success, depending on the particular time period in which they lived there. The ecological concept of Adapt or Perish is particularly appropriate for any culture that has ever tried to live in the American Southwest. In the next section we will focus on how drought or the lack thereof influenced the rise and fall of the Chacoan Phenomenon. But first, a few comments about Figure 2.

Archaeological research on the Chacoan Phenomenon has identified various time periods of drought, some long, some short, some local, some widespread. In looking at the graph in Figure 2 its obvious that fluctuations in precipitation in Northern New Mexico seem to be the rule rather than the exception. However, there have been two periods of drought that most researchers tend to agree on as being significant during the time periods of Chaco and Aztec – the first being an extended period of drought between 1120 and 1150 (some research suggests 1180), and a second major drought period between 1275 and 1300. In comparing these droughts with the rise, decline, and fall dates of Chaco and Aztec, it must be kept in mind that the graph is showing total annual precipitation in which both winter and summer rainfall are combined. Variations in seasonal rainfall (summer vs winter) cannot be determined. This is a critical point in considering the impact of climate change upon the Chacoan Phenomenon because the success or failure of farming and harvests at that time was completely dependent upon the Summer Southwest Monsoon rains, which can be notoriously variable from year to year, both in terms of time and location. How major changes in climate might have affected the Monsoon rains is little known.


This section discusses this writer’s speculative proposition that the two periods of drought shown in Figure 2 could indeed have been the root cause or catalyst that triggered the ultimate collapse and abandonment of the Chacoan World. Central to this proposition is Lekson’s 2015 proposal that the Chacoan political/social/government system as discussed above was essentially a modified version of the Mesoamerican Altepetl System consisting of Noble rulers living in Great Houses governing commoner farmers and labors, who paid tribute or taxes through goods (such as a portion of yearly harvest) or labor.

The Altepetl System as developed in Mesoamerica worked well there for hundreds of years from the Post Classic Period on (900-1519), and with some possible local adaptation by the Chaco Nobles, would have worked well during the height of the Medieval Warm Period at Chaco during the boom years of construction, expansion, and population growth when the climate was warm and precipitation plentiful. Then beginning around 1120 a series of droughts ensued during a period of climate instability for 30-60 years during which summer rains and other weather factors became increasingly unreliable as the global climate began to cool. Dry farming on the mesa tops, which had become possible at the height of the Medieval Warm Period, now became untenable, and the summer monsoon rains, which are always highly variable from year to year in terms of how much rain any specific area will receive, became even less dependable. The Major Nobles now had a problem, one that was not going to go away …

The problem was that their far flung 150-member atlepetl system had been constructed around the concept that in any given year, enough of the individual Outlier Great House altepetls would get enough rain for a successful harvest so that overall, the Total Choacan Summer Harvest would have a sufficient surplus to feed everyone in the Chaco System within the 150 kilometer (90 mile) radius of Great House Outliers, which operated on the Chaco Subsistence Economy. Those Outlier Altepetls that had not received rain from the increasingly less dependable Summer Monsoon did not have to worry, but could remain secure in the understanding that not only would they be fed that winter from the Food Bank Surplus in Chaco Center, but, if necessary, they would also be provided with seeds for the coming year’s planting!

But then, as the droughts increased in frequency and severity, came the years when the critical threshold was reached where the number of Great House Outliers with harvest failures exceeded the number of successful Outlier harvests, and the Food Bank Surplus in Chaco Center could not meet the Overall Demand. The Chaco System and the all knowing, all powerful and heretofore benevolent Nobles’ credibility was failing. What could the Nobles possibly do?

The rest of this speculative scenario is not hard to envision. What is known from the archaeological record as Lekson (2015) relates, and Turner and Turner (1999), and Kohler, et al. (2014)5 document is that during Chaco’s time, and especially in the later decades of the interval between 1020 and 1180, there were instances in the Chaco World of extreme violence ranging from individual killings or sacrifice to massacres of whole communities – from infants to the aged – being executed, dismembered, and in some cases even eaten, their bones then tossed into an empty room or kiva. Was this violence done under orders or direction of the Nobles, or was it just intra-Outlier hunger-driven, mob-violence warfare? A review of the nature of the religious component of the Chaco Culture as discussed above would suggest the former, especially when one considers that 6 out of the 76 sites studied by Turner and Turner were in Chaco Center in Chaco Canyon that included both extreme violence and cannibalism, some of which was found within the Great Houses.

Paquime Ruins Mexico

Paquime Ruins, Casas Grandes, Chihuahua Mexico

It is conceivable that when the suggested Noble-instigated and directed sacrifice, intimidation by dismemberment, and even worse, failed to increase crop production among the farming Commoners, and whole Outlier villages were abandoned as Commoners fled en masse during the night, in terror, to the East, West, and South, that the Major Nobles at Chaco Center may have seen the need for a new course of action. Eventually they may have come to the conclusion that maybe the failing harvests were the result of the climate after all, and not the fault of lazy, incompetent Commoner farmers, and that they should move Chaco Center to Aztec where the year-around waters of the Animas River could be used to irrigate and ensure dependable harvests. Which they did around 1110.

After the move to Aztec, as Lekson (2015) relates, apparently things were more peaceful between 1180 and 1260. Possibly the irrigated fields produced better and more reliable harvests, and, from Figure 2, after 1180 there appears to be an increase in rain until about 1250. If overall conditions did improve during this time, perhaps the Commoner’s faith in the wisdom and power of the Nobles over the weather, as well as the overall Chacoan System may also have been restored. That is until around 1275, when the droughts and precipitous global cooling recommenced in earnest, lasting until 1300. During this time period extreme violence, now more in the form of warfare, is again found in the Chacoan World between 1260 and 1280 (Kohler,, 2014), with communities massing together on defensible mesa tops or within cliff dwellings for safety. The chaos of these times was systemic with the eventual result of complete cultural collapse with both Nobles and Commoners alike abandoning the Four Corners area en masse by the tens of thousands. The Chaco Phenomenon was over.

Casas Grades, Chihuahua

T-shaped door at Paquime Ruins, Casas Grandes, Chihuahua Mexico

Paquime Ruins Chihuahua

Macaw raising pens at Paquime Ruins, Casas Grandes, Chihuahua, Mexico

During the period of Collapse and Abandonment of the Chaco/Aztec System around 1275-1280, and perhaps earlier during the move from Chaco to Aztec, Lekson (2015) contends that numerous Noble families headed due south along what he terms the Chaco Meridian where they would resume noble opportunities in the new emerging capital city of Paquime in Casas Grandes, Chihuahua, Mexico, 670 km (400 miles) south of Chaco Canyon. The evidence for a Chaco/Aztec/Paquime connection is a fascinating story in itself, and is the primary focus of Lekson’s 2015 book The Chaco Meridian.

During those turbulent times, the Commoners that fled or survived during the various Noble inflicted traumas during the latter years of Chaco, and the later warfare during the final collapse of Aztec, either migrated to points unknown or stayed in the general area to found new, more egalitarian, farming pueblos both to the west, south, and east of the Chaco/Aztec region, as represented by the Hopi, Zuni, and Acoma Pueblos of today.


The above summary of the Rise and Fall of the Chaco Phenomenon is a mixture of well-researched and documented archaeological fact, plus a heavy dose of follow-the-dots type reasoned conclusions and assumptions, as well as a little unabashed speculation. Quite often in archaeology, as in geology, the hard data that is found often raises more questions than it answers. And certainly this is the case with the Gila Cliff Dwellings. While there are important evidencial facts and clues from the Chaco Phenomenon which can shed some new light on the Key Questions posed in Part 1 of this blog regarding the People of the Gila Cliff Dwellings, the new evidence, indeed, raises a whole new set of questions.

The Key Questions Regarding the Gila Cliff Dwellers

Who were these Cliff Dwellers anyway and what were they like?

Convincing evidence, as summarized in this blog, supports the argument that the Gila Cliff Dwellers were Chacoan Nobles. Primary evidence for this fact is the abundance of prestige-economy marine shell jewelry, 26 macaw feathers, and 1 macaw skull; plus the architectural evidence in the commanding presence of a T-shaped door that for all intents and purposes says “We Are Chacoan”. If they were Nobles, then the evidence from Chaco also strongly suggests that they probably did not build the dwellings, farm the fields near the TJ Ruins, gather wild edible plants, or cook their own meals … Chacoan Nobles didn’t do such things; they had commoners or slaves to do this work.

Where did they come from?

Because the construction date of the Cliff Dwellings (1276-1287) as known from tree ring dating of the roofing vigas, corresponds exactly to the time of the Great Drought of 1275-1300 and the final Collapse of the Chacoan social and political system, it is considered most probable that the Gila Cliff Dwellers came either from an Outlier to the north or possibly from Aztec. Because of the abundance of Tularosa Phase pottery found in the Cliff Dwellings, the type locality for which is the Aragon/Reserve area 50 miles to the north, a southern Outlier would seem more likely than further north in Aztec. Although, a related fact is that Chacoan Nobles did not make their own pottery, so they could have come from Aztec and simply used locally made pottery, either imported from the Aragon/Reserve area or possibly made 1-1/2 miles away at the TJ Ruin.

Why did they come, and why did they choose to stay in dark, cold caves as opposed to the large TJ Ruin?

Based on the construction dates and suggested short-term occupation of the Gila Cliff Dwellings relative to the current understanding of the time and events of the final collapse of the Choacan social and political system, it is highly likely that the Nobles were fleeing the “Troubles up North” as suggested in Part 1 of this blog. As discussed above, Lekson (2015) makes a strong case that following the final collapse of the Chacoan System many of the Noble families left their failing system of increasingly oppressive rule over the Commoners, and moved south to Paguime at Casas Grandes, Chihuahua, Mexico.

Were there people living in the TJ Ruin site at the time, and if so what was their relationship with the Cliff Dwellers?

Only the formal excavation of the TJ Ruin could possibly provide definitive answers to this question. However, the strong evidence that the Gila Cliff Dwellers were Chacoan Nobles, and that Chacoan Nobles didn’t construct buildings, or farm the fields, etc., does support the possibility that the TJ Ruin was inhabited at the time of the Dwellings by someone, perhaps a reduced holdover population remaining from TJ Ruin’s height of occupation, or alternately a group of loyal Commoners of various types who accompanied the Nobles on their flight from the Chaco World who could have taken up residence in the abandoned TJ pueblos and farmed the adjacent fields.

Why did they stay such a short time? (as suggested by lack of adult burials, lack of trash, lack of building modifications and additions), and Why did they leave?

The presence of Noble prestige economy goods such as abundant marine shell jewelry, macaw feathers, and the skull of at least one live macaw being left behind could suggest a very sudden rather than a planned departure from the Cliff Dwellings, as these exotic objects and the T-shaped doors were the only proof of their Noble status. Did the “Troubles Up North” somehow catch up with them, forcing them to flee in the middle of the night? Also, as mentioned in Part 1 of this blog, large caches of stored maize in the form of cobs, were also found in the Cliff Dwellings, also suggesting an unanticipated departure. This sort of complete abandonment of personal goods and stored foodstuffs was a common archaeological discovery in the Aztec area, particularly in the Cliff Dwellings, during the last decades of the Collapse and Abandonment.

Where did they go?

Recent archaeological research at the Paguime Ruins and the surrounding Casas Grande area in Mexico, and the San Juan Basin area surrounding Aztec, have strengthened Lekson’s proposed connection between the collapse of the Chaco/Aztec Culture and the sudden emergence of the Paquime Culture. New analyses regarding the beginning of construction for the initial major buildings at Paquime yield dates of 1250 to 1300, which corresponds to the final collapse at Chaco and Aztec. Looking past the initial observation that the 4- to 5-story Paquime buildings are constructed of adobe while those at Chaco and Aztec are of stacked stone masonry, many architectural similarities between the two areas exist, such as the iconic T-shaped doors of Chaco and Aztec. Also, Paquime was very much involved with the prestige economy, and over time became a major center for the production, manufacture, and distribution of prestige economy goods, such as live macaws and macaw feathers, marine shell jewelry, copper bells, pottery, etc.

Perhaps the final collapse and abandonment of the Chacoan/AztecSystem is best summed up by Lekson (2015), when, after describing how the remaining Commoners moved east and west beyond the Nobles reach to reinvent themselves as communal, egalitarian farming Pueblos, he concludes by saying “scores of noble families, after many generations ruling, wanted nothing of the new egalitarian ethos. They sought new commoners to rule – that was their job on earth. There were no takers in the north, so they moved south – along the meridian.”

Research on ancient north–south trade routes used by prehistoric Native Americans indicates several possible routes leading south along the Meridian that the migrating/fleeing Nobles might have taken between Aztec and Chaco and Paquime. It is quite possible that one of them passed through TJ Ruin and the Gila Cliff Dwellings.

gila cliff dwellings new mexico

We Are Chacoan


1. Lekson, S.H., 2015, The Chaco Meridian. Rowman & Littlefield, 257 pp.,

2. Turner, C., and Turner, 1999, Man Corn: Cannibalism and Violence in the Prehistoric American Southwest.The University of Utah Press, 547 pages

3. Ljungqvist, F.C, 2010: A New Reconstruction of Temperature Variability in the Extra-Tropical Northern hemisphere During the Last Two Millennia. Geografiska Annaler, 92 A (3): pp.339-351

4. Grissino-Mayer, Henri D., 1996, A 2,129 Year Reconstruction of Precipitation for Northwestern New Mexico, USA, Tree Rings, Environment and Humanity, ed. J. S. Dean, D. M. Meko and T.W. Swetnam, Radiocarbon, pp. 191-204

5. Kohler, T.A. et al., 2015, The Better Angels of Their Nature: Declining Violence Through Time Among Prehispanic Farmers of the Pueblo Southwest, American Antiquity 79(3), 2014, pp. 444-464

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