The Large Cliff Top Pueblos at Mesa Verde, Colorado and Treeflow Data from Lees Ferry, Arizona

Guest essay by Samuel I Outcalt

The Data: The major tourist attractions at Mesa Verde National Park (near Cortez, Colorado) are the large cliff top pueblos inhabited by the Anasazi between 1128 and 1273 AD. To explore the relationship between the Anasazi occupancy of these large pueblos and climate change a 101 year center weighted moving average filter was applied to the Annual Treeflow Discharge Estimate of the Colorado River at Lees Ferry, Arizona (180 miles due west). These discharge estimates were calculated using the parameters derived from the linear regression of annual modern stream discharge [dependent variable] and modern regional tree ring data sets [independent variables].

The regression parameters were then used to estimate stream discharge at the gage site for length of the tree ring records. The explained variance of the tree ring data sets used in this reconstruction varied between 57% and 77%. The reconstruction is therefore noisy. The application of the century length filter attenuated high frequency noise in the annual data. The normalized record is displayed below as Figure 1.


Figure 1. The normalized filtered Treeflow Estimate at Lees Ferry. Arizona. Anasazi activity is noted and the linear trends of the record during the Medieval Warm Period and Little Ice Age are displayed.

Figure 1 indicates that the large pueblo occupancy was limited to a single wet regime near the end of the Medieval Warm Period. When the Colorado River discharge estimate declined to the approximate level of the large pueblo construction in 1128 AD the Anasazi abandon Mesa Verde in 1273 AD.

The Conclusion: The Treeflow Discharge estimate from Lees Ferry supports the hypothesis that evacuation of Mesa Verde and other Anasazi sites in the Colorado Plateau were a response to a regional drought, which reduced the discharge of the Colorado River to the west. It is interesting to note that the Colorado River discharge increased during the Medieval Warm Period and declined during the Little Ice Age.


Treeflow Data for many sites in the contiguous United States are posted at


42 thoughts on “The Large Cliff Top Pueblos at Mesa Verde, Colorado and Treeflow Data from Lees Ferry, Arizona

  1. Noisy, noisy. Did they move from cliffside to mesa top as a response to drying, then abandon both after the next dry spell?

    • No, in response to opportunity, and then the withering away of vegetation. Cool dry air makes droughts, not warm and wet.

    • I can see what happened, those large tree rings were global warming, then they decided the earth was at a tipping point, threw themselves off the cliff, saving the earth and returning the climate to normal. ( sarc )

  2. kim, that is a very good question. When they abandoned the mesa tops did they flee the region or move down into the canyons and start the cliff dwellings?

    • Having just been in New Mexico just North of Santa Fe Native Americans down there told me that the Mesa Verde (and Chaco Canyon) people moved down to New Mexico. The New Mexico Native Americans abandoned their own pueblos for the same reason, drought, in about 1600 AD and moved down to the river valleys where they still are today.

      • Anasazi cannibalism has been variously attributed to worsening climatic conditions, to the importation into the region of Meso-American Indian culture & to indigenous practices.

    • You often hear that Anasazi cliff dwellings were built for military defense reasons. BALDERDASH!

      The reason the dwellings moved from the mesa tops down into the cliff openings is because the half-arch cave openings are created by quasi-persistent water percolation which, in seasonal freeze/thaw cycles, slowly separate rock from rock and expands openings. This percolated ground water then pools at the back of the larger openings and caves, and provided a sparse but steady source of water that enabled their civilization to survive for a longer period. When the drought persisted long enough to dry up even the ground water percolating down, they had to leave.That’s my hypothesis, and I’m sticking to it until I hear a better one.

      • From what I’ve seen there can be little doubt that the cliff dwellings were defensive. They were inaccessible to the unwelcome. The grain was stored in the cliffs, so that the only period of vulnerability was harvest time. At some point around 600 years ago Athabascans came down from Canada and lived by hunting and raiding, making life for the Anasazi difficult. It just didn’t pay to farm only to see your crop go to your enemies. –AGF

  3. First, Samuel, thanks for all of your work. However, I don’t understand your claim. When the Anasazi abandoned their dwellings, according to you it was wetter than when they built their dwellings … how does that work?

    Also, you are using a 101-year centered filter. This takes information from as far as fifty years into the future. In other words, your filter is showing future wet-dry periods, as well as past and present periods. This makes any conclusions … well … preternatural. In other words, your claim is that the Indians moved in part because of droughts that hadn’t happened yet …

    Finally, a “boxcar” filter (an unweighted moving average) such as the one you have used is one of the worst kinds of filters, because it will alter and even invert the underlying data. I discussed this problem in my post Sunny Spots Along the Parana River.

    Were it me, I’d use a trailing Gaussian filter. This weights the more recent data more heavily than the data further in the past.

    Please be clear that I’m not listing ways that your analysis is wrong. I’m listing ways that you can improve your analysis.

    Best regards,


    • WIllis, the estimated discharge at the “time of abandonment” is very slightly less than the run off estimated at the time of occupation. Whether the modeled discharge means anything at all is a different question. Assuming that it does mean something, given that these dates are tree-ring dates, then the “abandonment date” reflects the time after which no additional construction or maintenance occurred on the pueblo. That could mean, without stretching very far, that the occupation carried on for some time afterward. The dependence on agriculture though puts serious bounds on how long they could hang around waiting for a better year.

      Maize agriculture pushes north into Fremont territory in Utah during the period between 700 CE and 1200 CE, but it never really takes off. About the time the Anasazi are retreating to the enclaves that survive into the historic period, maize farming among the Fremont people disappears altogether. Apparently they gave up farming as a bad idea.

      • I should have mentioned that looking closely at Samuel’s graph, red trend line does not mark the span of the Anasazi at Mesa Verde. Samuel has indicated the start and stop dates separately.

    • You can at least see (if you squint just right) the higher frequency in long droughts prior to 1550, that so many other researchers have concluded. Or maybe it would be more appropriate to say that the droughts that did occur post-1550 were less severe.

    • Long ago I had developed a forward / backward FFT filter. After the initial FFT the unwanted wavelengths were set to zero and the FFT applied again. In my old age I no longer have access to that software which ran on DOS. You can easily download the data from the website and compare the filters using the same data. That would make an interesting post.

      Best Wishes

      [Ah, but that assumes the others reading your comments know what your site is. .mod]

    • Thanks you Willis. That was my first thought on seeing this too.

      The running mean “filter” has a negative peak meaning that it inverts any variations around that frequency. From memory it’s window length /1.43

      101/1.43 is about 70 years. So the major climate variability of circa 60 will get turned upside down. Then he fits “trends” to arbitrarily chosen bit of the data.

      This is sadly so typical of the kind of incompetent garbage that the field of climatology seems to specialise in. The author does not appear to be a warmist but his data processing is of typical quality for the this field.

      At least he provided a link to data this time, so that a plus.

  4. So shortly, say 10-20 years, after abandoning Mesa Verde would have been a good time to move back in, right? Is that what the graph is saying? If so, I wonder why no one did so, or at least not that I’ve heard/read.

    • I’ve often wondered this myself. These were relatively nice permanent homes that anyone could have moved into at anytime after their abandonment, but apparently there is no evidence that anyone ever did.

      • There are indications in the archaeological remains that outsiders, possibly Toltec from central Mexico due to droughts there.

  5. Humans (and other animals) require regular hydration … it would only take a matter of hours if not days to decamp once a river/creek/spring stopped flowing and puddles began drying out. A 100-year filter effectively filters out the “noise” of such short-frequency, life-threatening events.

  6. My recollection from my visit there a few years back was that maize was the primary crop from which they fed livestock and poultry. The climate became inhospitable due to colder temperatures. Crop failures led to starvation and fighting. It is still too cold at these elevations for crops such as corn.

  7. The explained variance of the tree ring data sets used in this reconstruction varied between 57% and 77%. The reconstruction is therefore noisy.

    Agreed. It is noisy. And that’s a problem for the conclusion.

    How long does a drought need to last to cause abandonment?
    Either they had water management (like the Indus Valley) and could survive indefinitely or they would be down and out after three bad harvests.

    With that noise they must have had three bad harvests. So they must have developed some means of water management – not unreasonable as it was done in the sub-continent 5000 years earlier.
    That brings a big question mark over the drought being the main cause of the abandonment in the end.
    And why didn’t people return in the next generation? JI asks that above(April 16, 2015 at 10:00 am) and it supports my main point.

    The answer to “How will the world end?” is always the same.
    Climate is not Culture

  8. I’d suggest that is difficult to draw comparisons between Mesa Verde and flow at Lee’s Ferry. While they may be only 180 miles apart, Lee’s Ferry incorporates flow from the entire Colorado River Basin, much of which is derived from snow melt in the Rockies. Mesa Verde is in the southernmost portion of this area (near Four Corners). See the map at

    Quite often the two areas are subject to completely different weather systems.

  9. Author in 1st para uses climate change incorrectly; the time period before industrialization was not related to human-caused warming (AGW). He should have stated Natural Climate Change for that period.
    This is just what I figured would happen – the smart liberal machine reverted to Climate Change (it wasn’t warming and the PDO shifted) from Global Warming. So now, most people are using Climate Change indiscriminately. And that puts Global Warming in the background, which would be the downfall of the agenda.

    • I was using “climate change” in the most general sense. Now “climate change” to many is a code for industrial induced global warming. Years ago I was giving a seminar at the UDEL and a student ask me if I believed in “global warming”. I replied that I didn’t wish to discuss religion with strangers..

  10. “Drouth” is a constant threat in Australia. There is always a ‘Drouth” somewhere in Australia. Sometimes there are also Droughts, which are very wide spread and persistent. They are however not related to Global Warming.

  11. From the figure, it is clear that from around 1600 to 2000, the change is flat.

    Dr. S. Jeevananda Reddy

  12. Averaged over the “West” there was a significant wet spell right in the middle of the supposed MWP drought:

    The “West” is a pretty big place and regional variations within it are significant. Here are the two iconic droughts of the twentieth century:

    Notice the very different conditions in these Palmer Drought Index simulations:

    Benson (2002) drilled Pyramid Lake, Mono Lake, Owens Lake, and some lake in New Mexico in the style of the Ocean Drilling Project. Here are his results:

    Nothing is easy in this business…

    • The Sonoran Desert is characterized by the annual double pulse of moister it receives. The winter rains from the Pacific, and the summer monsoonal rains from the Gulf of Mexico. In Arizona, this area is made up of the Verde/Salt/Gila water sheds. The Colorado drains the Colorado Plateau which has a different climatic regime.

      • Yes Desert, that is a general problem with averages. However, having spent a good amount of time rowing the Colorado River, I can attest that monsoonal rains have a dramatic effect on its flows, both above and below Lake Powell.

      • Gym,
        Monsoonal effects on the Colorado Plateau are sporadic in comparison to the effects on the Sonoran Desert. I am not saying that there is no effect. My point was more about the different climatic regimes of the two areas, one dominated by snow pack melt, and one by monsoonal rains. The Monsoon defines the Sonoran in a way that it does not define the Plateau. If you don’t believe me, look at any pre CAGW text on the subject. BTW, the name DesertYote == Canis latrans mearnsi, is no accident. I have spent my life exploring and studying the aquatic habitats of the Sonoran Desert and Colorado Plateau, not just some paddle trips on the Colorado. A few times I had to high tail my butt out of a canyon on hearing thunder at 3 in the afternoon. And yes, the Colorado Plateau is more dangerous in this regard. It might not get it as often, but when it does, it is awesome.

  13. There were other complicating factors in the Anasazi abandonment besides drought. At nearby Navajo National Monument in northeast Arizona, where I worked as a park ranger in the late ’60s-early ’70s, there is evidence of extensive sheet erosion occurring in the latter 1000s terminated by a dramatic gully-cutting episode around 1100, at which point the Laguna Creek Canyon area was abandoned. Shortly thereafter, however, it was re-colonized by the cliff-dwellers, who were probably the same people. In my Harvard masters thesis, I argued that the sheet erosion bespoke increasingly intensive maize agriculture in the canyon bottoms, which culminated in the gully erosion when farming activity eventually breached the protective riparian gallery forests along the stream courses. This coincided with the first great drought, which brought intense summer rainstorms, resulting in the deep gully erosion, which dropped the water table, rendering farming impossible, and abandonment soon followed. The cliff dwellers then recolonized the canyons, and their smaller population was able to eke out a living until the next big drought, which resulted in final abandonment around 1300. The canyons then began to reaggrade, and the Navajo came in in the 1500s, and lived there successfully until the US government gave them sheep, which overgrazed the canyons, leading to a second episode of deep gully erosion in 1909. When I interviewed older Navajos about the erosion, they refused to consider the possibility that overgrazing by their sheep was the cause. “The canyons were bewitched!” they said.

  14. I live in Colorado, and I’ve done extensive reading about the Anasazi, as well as just about everything else in this state. I’ve visited Mesa Verde, Chimney Rock, and several other Anasazi locations, some more than once. Let’s get a few points out there that need to be discussed:

    1) The Anasazi region is a LONG way (climate-wise) from the Colorado River basin. The drainage basin they should have evaluated (if possible) would be the San Juan River basin and the streams that feed it, especially the Animas River and the Mancos River. All of the streams that carved the mesa and canyon lands used by the Anasazi flow eventually into the San Juan. The San Juan River joins the Colorado in Utah at the Glen Canyon NRA, after dipping down into New Mexico. The Colorado River basin begins along the Continental Divide in northern Colorado, runs more or lest wsw through Grand Junction, then down toward Arizona. There is a major feeder river (the Gunnison) that flows into the Colorado at Grand Junction. The Gunnison brings water from the northern and western slope of the Continental divide. The San Juan and its tributaries originate in the San Juan Uplift, which forms an arc running east/southeast/south from Silverton, around Pagosa Springs, and down to the New Mexico Border near Chama. The San Juan joins a couple of dozen miles north of the Utah/Arizona state line.

    2) The major crops of the Anasazi in Mesa Verde were squash and gourds, with corn only in the lower portions of the canyon. They also gathered pinion nuts from the many pines in the area, and other local vegetation. There are other mountaintop dwellings in numerous places, and even a few other cliff dwellings. There is evidence of terracing, canals, catch-basins, and other water management structures. There were three reasons to build in the big bays and cliffs in the canyons – the areas were protected (from the elements as well as from their enemies), there was room to bring the majority of the tribe into one area, and religious reasons (see Chimney Rock National Architectural Site).

    3) Mesa Verde, Chimney Rock, and several other areas were feeder areas for Chaco Canyon. Once the great drought began to reduce stream flows, logs and food offerings from Chimney Rock and other areas could no longer be floated downstream on the San Juan to modern-day Bloomfield, where they were gathered and carried along the Great North Road to Chaco Canyon. There was also an apparent religious upheaval in the area at about the same time. The Mesa Verde area was probably abandoned because a combination of drought, disease (it didn’t get cold enough in the winter to kill some pests – approximately the same thing that’s currently happening with the pine beetle), and religious upheaval drove them from the area.

  15. No. The Athabascans came down and drove them out. They were, and are, part of the Iroquois league, a tribal league that took over more land then Alexander the Great. Thankfully, most of them have now settled down and have become great citizens of Canada. The Anasazi were just fodder for them way back then.

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