MESA VERDE NATIONAL PARK, Colo. — Almost a century after these ancient Indian ruins became a national park in 1906, strange earthen formations near the cliff and mesa-top dwellings continued to puzzle and divide scientists, until recently.
One mysterious dirt mound, 200 feet across, rises 16 feet above the floor of Morefield Canyon. A 1,400-foot path or channel extends from it, making it resemble an upside-down frying pan with a long, flat handle.
And then there was the large depression in the park's heart on Chapin Mesa. It was labeled for years as either a prehistoric amphitheater or perhaps an impoundment of water — nicknamed Mummy Lake — with no known source of water.
Now, scientists know the depression was part of an elaborate water storage system and have dubbed it Far View Reservoir. And Morefield Canyon's elevated mound, which does not resemble a reservoir, was a storage facility that could have held 120,000 gallons of water.
After a decade of investigation just ended by a large team of private water engineers and government scientists, it is recognized that the Ancestral Puebloans who lived here until 1300 were remarkable water engineers.
"They knew how to manage water," says Eric Bikis of Wright Water Engineers Inc. in Durango. "They were ingen- ious."
The people of this high desert, without benefit of metals, wheels or written language, maintained at least four massive waterworks from A.D. 750 to 1180 to survive the devastating droughts of the Four Corners region. The last of these works studied, a large mound dubbed Box Elder Reservoir, wasn't discovered until a 2002 wildfire burned off a dense, high carpet of sagebrush.
But scientists had been confused for decades over how the giant mud pie in Morefield Canyon, high above the bed of a desert stream that rarely flows, could have served as a reservoir. Many guessed it was a terrace for ceremonial dances.
In the late 1990s, Denver water engineer and author Kenneth Wright, known for his studies on ancient Incan waterworks in the Peruvian Andes, collaborated with engineers and government researchers to cut a deep trench through the Mesa Verde mound and finally solve the mystery.
The Puebloans, the team concluded, had started with a shallow depression that was originally along the bottom of an intermittent stream. They used the small impoundment, and others such as Far View, to capture water during rare big storms, which occur several years apart, Bikis says.
These floods eventually filled the reservoirs with as much sediment as water, and ancient workers had to scoop them out. In Morefield Canyon, the reservoir bottom slowly rose above the canyon floor despite some 350 years of scooping. The Puebloans compensated for the reservoir's growing height by creating a long canal to divert flood flows. It had the proper gradient to continue to fill the rising reservoir.
A thousand years before this was a park, Wright says, Mesa Verde was an astounding collection of public construction projects, from the stone cliff dwellings to the newly appreciated water system.
Modern engineers recently honored the Puebloans' Mesa Verde reservoirs by naming them a Historic Civil Engineering Landmark.
"The Ancestral Puebloans that populated the riverless mesa top conquered the impossible by creating a water system to sustain their domestic and agricultural needs," says Patricia Galloway, president of the American Society of Civil Engineers.