The Anasazi: Colorado's first irrigators

The Anasazi: Colorado's first irrigators

From 1995 to 2003, Ken and Ruth Wright of Boulder helped excavate four flat "dirt piles" at Mesa Verde National Park. The Wrights discovered that the Anasazi were Colorado's first public works' engineers. The "dirt piles" are actually filled-in water storage ponds which the Anasazi dug in drainages around 750AD and dredged frequently, using sticks, antlers, baskets and stones. Over the years, these ponds silted up, but instead of abandoning them, the Anasazi dug ditches and diverted waters into the ponds from further upstream on the drainage.

Right, Clockwise from top:

Anasazi at Mesa Verde depended on corn, beans and squash to feed their large populations. How could thousands survive in an area with average annual rainfall of 15 inches?

The Wright Paleohydrological Institute team gathers evidence from a 16-foot deep excavation trench at Morefield Reservoir. Sediment layers, pollen samples, pottery shards and anoxic soils that could only have existed in water saturated conditions prove a reservoir existed at this site for more than 350 years.

Because of these reservoirs, Mesa Verde populations survived climate change in 900AD, when the entire southwest became much drier. However, an extremely severe drought from 1135 to 1180 caused the abandonment of the reservoirs. The Anasazi then depended solely on water from springs until another drought in 1275 caused them to abandon Mesa Verde for the more certain water supplies of the Rio Grande. By 1300, Mesa Verde was completely deserted. From Citizen's Guide to Colorado's Water Heritage, Colorado Foundation for Water Education.

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