From Yahoo! (Joseph Castro):
Mummy Lake is a sandstone-lined circular pit that was originally 90 feet (27.5 meters) across and 22 feet (6.65 m) deep. In 1917, American naturalist Jesse Walter Fewkes pegged the structure as a prehistoric water reservoir. Several subsequent studies of Mummy Lake have also supported this view, leading the National Parks Service to officially name the structure “Far View Reservoir” in 2006. (Far View refers to the group of archaeological structures located on the northern part of the park’s Chapin Mesa ridge, where Mummy Lake is also situated.)
In the new study, researchers analyzed the hydrologic, topographic, climatic and sedimentary features of Mummy Lake and the surrounding cliff area. They concluded that, contrary to what previous research had determined, the pit wouldn’t have effectively collected or distributed water…
“The fundamental problem with Mummy Lake is that it’s on a ridge,” said study lead author Larry Benson, an emeritus research scientist for the U.S. Geological Survey and adjunct curator of anthropology at the University of Colorado Museum of Natural History. “It’s hard to believe that Native Americans who understood the landscape and were in need of water would have decided to build a reservoir on that ridge.”[…]
To test this reservoir theory, Benson and his colleagues first analyzed the topography and hydrology of the ridge using GPS surveys, high-resolution imagery and digital elevation models.
They found that the ditches leading from Mummy Lake to the southern structures couldn’t have functioned as water canals or irrigation distribution systems. The ditches would have easily spilled water over the canyon edge at various points if it didn’t have walls controlling the water flow (which don’t appear to have existed).
Next, the team used climate models to investigate Mummy Lake’s potential to store water. They found that even in the wettest year on record, 1941, the pit would have gotten less than a foot of water from winter and spring precipitation by the end of April. This water would have completely evaporated by the end of July, when it’s most needed for crops.
The researchers then tested if a hypothetical feeder ditch could actually provide Mummy Lake with water. “The engineering and sediment transport work showed that any water in the ditch would start moving so much dirt that it would block the path,” Benson said. That is, soil would have quickly clogged the ditch after regular rainfall, preventing the water from reaching Mummy Lake…
Benson and his colleagues propose Mummy Lake is an unroofed ceremonial structure, not unlike the ancient kivas and plazas elsewhere in the Southwest. They noted that the structure is similar in size to a great kiva found at a Pueblohistorical site near Zuni, N.M. It also resembles a ball court and amphitheater at the Puebloan village of Wupatki in Arizona — interestingly, Fewkes also thought these two structures were reservoirs.
Furthermore, the ditches connecting Mummy Lake to Far View Village, Spruce Tree House and Cliff Palace aren’t canals to transport water, but rather Chacoan ceremony roads with similar dimensions to Chacoan roads that exist at other sites in the San Juan Basin, the researchers argue.
Two decades ago, researchers studying the Manuelito Canyon Community of New Mexico discovered the Ancestral Puebloan population had an evolving ritual landscape. Over the centuries, the Manuelito people relocated the ritual focus of their community several times. Each time they moved, they built ceremonial roads to connect their retired great houses and great kivas to the new complexes.
Benson and his colleagues suspect the same thing happened at Mesa Verde. Mummy Lake was built as early as A.D. 900, around the same time as the rest of the Far View group of structures; Cliff Palace and Spruce Tree House, on the other hand, date to the early 1200s. The researchers think the community relocated to the latter structures between A.D. 1225 and 1250, and connected their past with their present using the ceremonial roads…
The study was detailed in the April issue of the Journal of Archaeological Science.
More San Juan River Basin coverage here.