Snowmastodon! Reservoir Project Unearths Fabulous Fossils

The Snowmass Water and Sanitation District makes a prehistoric discovery in the Rocky Mountains
Snowmastodon! Reservoir Project Unearths Fabulous Fossils
Artist's rendition of an American mastodon (Mammut americanum), the most numerous of the megafauna discovered in the Snowmass Village fossil site.

To the Snowmass (Colorado) Water and Sanitation District it’s known as the Ziegler Reservoir Enlargement Project. To scientists at the Denver Museum of Nature and Science it’s known as one of the world’s most significant finds of mastodon fossils. 

The district, located roughly 200 miles west of Denver, had planned for some time to reduce its reliance on live flows from Snowmass Creek Basin as a primary water source. SWSD takes its water from high mountain streams. Some of the water is stored at the Ziegler Reservoir, so the district — which supplies a population that fluctuates from 2,500 to 18,000, depending on the season — can call on reserves when flows are minimal.

“We performed hydrographic modeling to determine the amount of water available to meet our needs,” says District Manager Kit Hamby. “We determined that building a reservoir to store creek water during peak flows was the most effective way to support growth. In 2008, we purchased the Ziegler Reservoir, which was an existing reservoir on the footprint of a glacial lake. However, it was only about 6 feet deep, so our aim was to enlarge it by digging out the bottom and rebuilding it with an earthen dam.” 

On Oct. 14, 2010, the first day of construction, bulldozer operator Jesse Steele of Gould Construction discovered the first prehistoric fossil. 

“I got a frantic call from the excavating company that they’d pushed up bones, and asking me to go down to see what they’d discovered,” says Hamby. “It turned out to be the bones of a juvenile female Columbian mammoth. I had that area fenced off and had a huge team of scientists from the Denver Museum of Nature and Science arrive within hours.” 

Work in the vicinity of the discovery was suspended immediately to allow scientists an opportunity to survey the site. Within 24 hours they uncovered fossils belonging to a rare American mastodon. The museum negotiated with the SWSD to continue work at the site, excavating fossils with the promise that the site would not be flooded before November 2011. 

“Apparently the site was so rich in finds because the glaciers pushed ice and debris on top of the site over a ridge, instead of scooping it out,” says Hamby. 

Dubbed the Snowmastodon Project, the big fossil dig included the efforts of scientists from the U.S. Geological Survey and more than a dozen other institutions. 

In the following year, scientists recovered almost 5,000 bones dating as far back as 150,000 years, including those belonging to giant bison, Ice Age camels, horses, a ground sloth, prehistoric deer and assorted reptiles and amphibians. 

“The U.S. Geological Survey also discovered pollen, leaf and soil samples that could give them solid leads about what the climate might have been like in this region 140,000 years ago,” says Hamby. 

Once the Snowmastodon Project was completed, the earthen dam reached completion and the reservoir was filled with water. 

“That’s actually a good thing for any remaining fossils at the site,” says Hamby. “Water cover preserved those fossils for 100,000 years, and any remaining specimens will be preserved for a potential future dig.” 

The SWSD, along with the Denver Museum and Gould Construction, were presented with History Colorado’s 2012 President’s Award for historical preservation.

Photo "American Mastadon" by Sergiodlarosa is licensed under CC-BY-SA-3.0


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