Was it a reservoir, a ceremonial plaza, or a ball court?

At Mesa Verde National Park, the Far View Reservoir ruin - also known as Mummy Lake - has long been a controversial mystery for archaeologists. A new study tries to settle the issue.

Since 1917, the prevailing view was that the large circular depression lined by sandstone walls was an ancient reservoir built as early as 900 A.D.

Sediment buildup behind a supposed intake canal fit the reservoir profile. A set of stairs into the structure suggested it was used by Ancestral Puebloans to collect stored water. Faint impressions of irrigation canals leaving the lake pointed to agricultural use.

"It fits nicely into our present day experience of dealing with drought by storing water," said Scott Travis, Mesa Verde's chief of research and resource management. "During heavy rains it does collect some water."

But archaeologist Larry Benson refutes the reservoir theory in a paper titled "Mummy Lake: An Unroofed Ceremonial Structure Within a Large-scale Ritual Landscape."

Published in the Journal of Archaeological Science, Benson hypothesizes that the function of Mummy Lake was for community ceremonies and was abandoned due to drought in the early 1200s.

Benson points to previous studies that ancient Southwest cultures periodically relocated their ceremonial structures, then linked them to newly constructed facilities by means of broad avenues.

"The avenue has previously been interpreted as an irrigation ditch fed by water impounded at Mummy Lake," writes Benson. "However, it conforms in every respect to alignments described as Chacoan roads."

A sturdy staircase, elaborate for its time, descends into Mummy Lake and is convincing evidence that is was a ceremonial plaza.

"The way the stairs were perfectly built suggests it was not just utilitarian," Travis said.

For several weeks this summer, Benson's crew was at the site studying landscape hydrology to disprove the reservoir theory.

Benson doubts the topography would have allowed for the reservoir to fill because it is on an elevated ridge.

A feeder ditch required to fill Mummy Lake from a larger basin has never been found, and two other so-called irrigation ditches would not have been capable of collecting and distributing water.

"Within a matter of seconds during a storm, sediment would have filled the hypothetical ditch, then forced the water over the cliff edge," Benson writes.

Benson redefines the irrigation canals as wide avenues that linked the Mummy Lake ritual plaza with neighboring Far View and Pipe Shrine Houses, and also to the farther away Cliff Palace and Sun Temple complexes.

"South of Mummy Lake, we found faint, straight swales that suggest roads," Travis said. "But the area is also a main terraced farming location that could have benefited from an irrigation canal."

A very intriguing explanation of Mummy Lake is that it could have been used as an ancient ball court. Ball courts have never been documented at Mesa Verde, and the closest one to the region is in the ancient Hohokam villages near Phoenix.

Travis said further excavation at Mummy Lake is not planned in the near future. He said if a floor structure could be found it would be a good clue for a ceremonial plaza or perhaps a ball court.

"Archaeologists love to argue about Mummy Lake," Travis said '"What do I think?' It could have been used for both ceremonies and water collection."

Since the Benson study, the park is considering adding interpretation panels at the site describing alternate theories. And lately, more documentary crews have been scheduling time at Mummy Lake to feature its mysteries.

"We have not heard the end of the Mummy Lake story," Travis said.