The Snowmastodon site, also known as the Ziegler Reservoir fossil site, is the location of an important Ice Age fossil excavation near Snowmass Village, Colorado. Fossils were first discovered on October 14, 2010, during the construction of a 5 hectares (12 acres) reservoir to supply Snowmass Village with water. Over the subsequent weeks, after an agreement had been reached to allow paleontological excavation, crews from the Denver Museum of Nature & Science and the U.S. Geological Survey worked along with the construction crews as more fossil material was uncovered. The site closed for five months over the winter, reopening May 15, 2011. Between May 15 and July 4, 2011, crews from the Denver Museum of Nature & Science conducted a large scale fossil excavation alongside construction crews building a dam for the reservoir. In total over 36,000 vertebrate fossils (including mammoths, mastodons, ground sloths, horses, camels and deer), more than 100 species of fossil invertebrates and over 100 species of fossil plants were found in sediments deposited by an alpine lake during the last interglacial period.
Discovery
The fossil site was discovered on October 14, 2010, by Gould Construction Inc. crews who had been employed by the Snowmass Water and Sanitation District (SWSD) to expand the Ziegler Reservoir and provide additional water supplies to the nearby town of Snowmass Village. While clearing the perimeter of the reservoir, bulldozer operator Jesse Steele unearthed the first animal bones. Recognizing them as possible fossils, Steele informed project foreman, Kent Olson. Olsen took the bones home and identified them as belonging to a mammoth using sources he found on the internet. The next morning, Kit Hamby, the district manager for the Snowmass Water and Sanitation District (SWSD), contacted a contractor from the Colorado Geological Survey who contacted the Denver Museum of Nature & Science (DMNS). The DMNS reached an agreement with the SWSD to allow the museum to excavate the fossils. Crews from the Denver Museum, U.S. Geological Survey, and several other institutions work alongside bulldozers for two weeks in order to salvage the increasing number of fossils being unearthed. The onset of winter caused the site to be closed for five months beginning November 15. When the excavation resumed on May 15, 2011, museum crews had 7 weeks to complete the excavation in order for the reservoir project to be completed on time. By the time excavation had been completed, the team consisting of more than 250 volunteers and 40 project scientists removed approximately 8000 cubic meters of sediment. Thousands of fossils were collected along with stratigraphic, geochronologic, palynologic, paleoentomologic, and paleobotanic data that was subsequently used to reconstruct the paleoecosystem at ancient Lake Ziegler.
Snowmastodon Project A $10.5 million dam for the reservoir was scheduled to be completed by mid-October 2011, with the site was expected to be underwater by November 2011. For that reason, any paleontological excavation had to be done quickly. The excavations were led by the Denver Museum of Nature & Science, together with the U.S. Geological Survey and scientists from at least 19 institutions. The Snowmastodon Project, as the efforts had been dubbed, cost approximately $1 million, including public outreach programs. Half of the costs were covered by grants and gifts to the museum, while the rest came from donations. The first scientific excavation officially began on November 2, 2010. It involved 67 workers from the Denver Museum of Nature & Science, and lasted 12 days. Preliminary efforts concluded on November 14, 2010, when the arrival of winter prevented any further excavation. The site and fossils left in situ were protected with frost-free barrier and the recovered fossils taken to the conservation laboratory of the DMNS. More than 600 bones and 130 plant, rock, and invertebrate samples were recovered, including the first mastodon skull ever recovered in Colorado (unearthed a mere day after the beginning of the excavation) and the first remains of a Jefferson's ground sloth to be found in the state. Other megafauna recovered included giant bison, two deer-like animals, and more mammoths. Excavations resumed during spring of 2011, from May 15 to July 4, with the support and permission of SWSD and the State of Colorado. By the end of July, the total number of bones recovered was around 36,000, from at least 52 different Ice Age vertebrate animals. Approximately 3,000 of them are believed to come from mastodons of both sexes and of varying ages, from infants to full adults. Other new animals recovered included an Ice Age camel, a horse, and various smaller vertebrates. A small excavation crew from the museum remained at the site, in the event further discoveries were made in the course of the dam construction. The speed at which the fossils were recovered (more or less seven weeks) is remarkable for a scientific dig of this size. Kirk R. Johnson, leader of the Snowmastodon Project on behalf of the Denver Museum of Nature & Science, told the New York Times, "The speed of this thing is so unlike normal science — from discovery to completion of one of the biggest digs ever in less than nine months." Scientists are not concerned now that the site is covered by water after completion of the reservoir expansion. Being underwater helps preserve the fossils and the reservoir can be drained if ever the need arises for additional excavations.
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