The American southwest is generally identified with a dry, hot climate, and not without reason. Large portions of it, including some of the cities best known to people elsewhere (such as Phoenix and Las Vegas), are in classic desert ecosystems, with extremely hot summers, very mild winters, and very low humidity year-round. Even in parts of the southwest that aren’t like that the summers are generally hot, and the humidity is generally low, so it’s understandable that a lot of people assume that snow, for example, is a foreign concept here.
That, however, is decidedly not the case in many parts of the southwest. One thing that people don’t often realize about this part of the country is that it’s at a pretty high elevation, and while in most parts of southern Arizona the southerly latitude tends to cancel out the cooling properties of the elevation, the parts of the southwest that are further north get quite cold at times. It snows every year in the northern parts of New Mexico and Arizona, as it does in Colorado and Utah, which are just a little bit further north. The more mountainous areas get a lot more snow than the lower basins, but “lower” is a relative term there; the elevation at the floor of Chaco Canyon, which is in the middle of the San Juan Basin, is 6200 feet above sea level.
So, it snows. Places like Chaco tend to only get a couple of inches at a time before strong winds move a storm on through, but sometimes a storm lingers and drops a lot more. This is one of those times.
It’s been snowing continuously now for at least fourteen hours. It was snowing when I got up before dawn, and it’s still snowing. The park was open, as it always is, but we had very few visitors. I’d estimate we’ve gotten at least six inches so far, quite possibly more, and this could continue all night.
This isn’t really a typical amount of snow, but neither is it a freak occurrence. We get snow here every year, mostly in December and January, much to the consternation of some visitors who assume that things here will be warm and sunny. Chaco visitors are a hardy breed, however, so they often show up anyway. We did have some visitors even today, though admittedly very few and mostly people who camped last night and were therefore here already.
The climate at Chaco Canyon is harsh, but not in the same way people often think about harsh climates. It doesn’t get as hot or as cold here for as long as in many other places. There are many drier places as well. What distinguishes Chaco, however, is the combination. The temperature hits both zero and 100 degrees Fahrenheit at least once almost every single year, and on top of that the annual precipitation has averaged between eight and nine inches over the past hundred years and about six inches over the past ten. Not the hottest, coldest or driest place in the world, by any means, but a pretty difficult place to live nonetheless.
One of the most frequent questions we get is whether the climate was different 1000 years ago, when the buildings of which we see impressive remains were built and the regional system centered on the canyon was reaching a remarkable level of sophistocation. The answer is no. There has been extensive research on the paleoclimatology of the San Juan Basin, and the clear result of that research has been that the overall climate hasn’t changed in several thousand years. There have been many fluctuations in temperature and precipitation on the order of years or decades, but the magnitude of those fluctuations over the past few centuries, including the Chacoan Era, has been well within the range of observed variation in historical times. That is, there were times when the Chacoans were here when the canyon was wetter than it is now, but there were also times when it was drier, and the differences were generally no greater than the (rather significant) variation in moisture over the past 100 years. People often find this surprising, since it’s only natural to assume that a society that built all this amazing stuff in this most unlikely place must have had much different conditions from what we see today, but I think it’s ultimately a testament to the technical and organizational skill of the Chacoans that they were able to pull off their impressive feats given the challenging environment they were working in. Why they were trying to do so much in such a difficult place is another question, of course, and an important one, but one that can wait for another post.