The Snowmastodon site, also known as the Snowmass Village fossil site or the Ziegler Reservoir fossil site, is a fossil excavation near Snowmass Village, Colorado. It was discovered on October 14, 2010, when construction workers building a reservoir dam to supply water to Snowmass Village uncovered fossil bones that turned out to belong to a young female mammoth. Official fossil excavations, organized by the Denver Museum of Nature and Science under the nickname "Snowmastodon Project," began on November 2, 2010. They ended, as agreed, on July 1, 2011, so that construction work could resume. During this short period, the project unearthed 4,826 bones from 26 different Ice Age vertebrates, including mammoths, mastodons, bisons, camels, a Pleistocene horse, and the first ground sloth ever found in Colorado.
The fossil site was discovered on October 14, 2010 by Gould Construction Inc. crews. They were working for 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 and project superintendent Kent Olson researched the Internet to identify the remains. They eventually correctly identified them as belonging to a mammoth. They unearthed approximately 20% more of the bones and notified the director of SWSD, Keith Hamby. SWSD quickly contacted the Denver Museum of Nature & Science (DMNS).
On October, 16, 2010, Dr. Ian Miller, the DMNS curator of paleontology sent a small team to investigate. Negotiations immediately began for museum excavation of the site after the initial survey. The original discovery, since identified to be a young female Columbian mammoth (Mammuthus columbi), was also donated to the museum on October 25, 2010. It was given the nickname of 'Snowy' after Snowmass Village.
On October 27, 2010, Kent Olson discovered the remains of a second animal. Initially thought to be another mammoth, it turned out to be a fossil of the rarer American mastodon (Mammut americanum). This discovery increased the importance of the site significantly, as previously, only three other mastodon fossils have ever been found in Colorado.
The Snowmastodon Project
Because the $10.5 million dam was scheduled to be completed by mid-October 2011, the site was expected to be underwater by November 2011, and 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 have been dubbed, will cost approximately $1 million, including public outreach programs. Half of this has already been covered by grants and gifts to the museum, while the rest is expected to come from donations.
The first excavation officially began on November 2, 2010. It involved 67 workers from the Denver Museum of Nature & Science working for a total of 18 days. The dig itself only lasted 12 days, ending on November 14, 2010 when the arrival of winter precluded any further efforts. 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 (Megalonyx jeffersonii) to be found in the state. Other megafauna recovered included giant bisons (Bison latifrons), two deer-like animals, and more mammoths.
Excavations were resumed during spring of 2011, from May 15 to July 1, 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 4,826, from at least 26 different Ice Age vertebrates. 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 (Camelops), a horse, and various smaller vertebrates.
A small excavation crew from the museum remained at the site, in case 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, overseer 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, however, are not overly concerned at the prospect that the site may be covered by water when the reservoir expansion is complete. Being underwater helps preserve the fossils better and the reservoir can be drained as needed if ever the need arises for additional excavations.
The find is considered one of the most important recent paleontological discoveries. It is one of the few high altitude Ice Age fossil sites, at 8,874 ft (2,705 m) above sea level, especially significant for preserving a snapshot of the diversity of the ecosystem in one place. The fossils recovered exhibit remarkable preservation. The plant matter is still green and beetle exoskeletons are still iridiscent. Scientists think there is a good chance that intact DNA can be recovered from some of the vertebrate fossils.
It is also considered the "finest mastodon site in the world" due to the large number of mastodon fossils recovered.
The National Geographic Society, which donated a $55,000 grant to the project, plans to feature the site in the National Geographic Magazine . The science television series Nova broadcast an episode  about the site in February, 2012.
Geochronology and paleoecology
The site is known to be more than 45,000 years old from initial radiocarbon dating. It is further estimated to be between 150,000 and 130,000 years old, coming from the Illinoian age of the Pleistocene epoch.
The area where the fossils were recovered was once the shores of an ancient small glacial lake. Sediment layers suggest an alternating warmer climate when forests grew on its shores and colder climates, when the lakeside became a tundra and thus above the treeline. It filled up around 50,000 to 100,000 years ago, becoming an alpine meadow. Finally, in the 1960s, the area was converted to a reservoir by R. Douglas Ziegler.
The total number of bones recovered is 4,826 including 49 tusks and 23 skulls. It comes from 7 large mammals (megafauna) and about 19 smaller vertebrates including otters, muskrats, voles, minks, chipmunks, bats, rabbits, beavers, mice, salamanders, frogs, lizards, snakes, fish, and birds.
- Columbian mammoth (Mammuthus columbi) - At least 3 individuals, including the first fossil recovered from the site (since nicknamed 'Snowy'). The Columbian mammoth is an extinct species of elephant of the Quaternary period that appeared in North America (in the present United States and as far south as Nicaragua and Honduras) during the late Pleistocene.
- American mastodon (Mammut americanum) - At least 30 individuals and comprises approximately 60% of the total number of fossil bones recovered. The American mastodon is an extinct North American proboscidean that lived from about 3.7 million years ago until about 10,000 BC. It was the last surviving member of the mastodon family.
- Jefferson's ground sloth (Megalonyx jeffersonii) - At least four individuals. The first remains of the species recovered in Colorado and the highest elevation occurrence recorded in North America. The Jefferson's ground sloth is an extinct species of giant ground sloth that lived from the Illinoian Stage of the Middle Pleistocene (150,000 years BP) through to the Rancholabrean of the Late Pleistocene (10,000 BC). Its closest living relatives are the two-toed tree sloths of the genus Choloepus.
- Giant bison (Bison latifrons) - At least 10 individuals. The giant bison is an extinct species of bison that lived in North America during the Pleistocene. It reached a shoulder height of 2.5 meters (8.5 feet), and had horns that spanned over 2 meters (6.5 feet).
- Deer - At least 3 individuals of indeterminate species.
- Tiger salamander (Ambystoma tigrinum) - Numerous individuals. It is an extant species of Mole Salamander.
- Camelops - A single tooth. Camelops is an extinct genus of camels that once roamed western North America. It disappeared at the end of the Pleistocene, about 10,000 years ago.
- Horse - A single foot bone from an indeterminate species of Equus.
- Denver Museum of Nature and Science
- List of fossil sites
- Pitkin County, Colorado
- Pleistocene megafauna
- Snowmass Village, Colorado
- Southern Rocky Mountains
- "Significant Fossil Find Unearthed in Colorado by Gould Construction". CU Engineering, University of Colorado. Retrieved July 8, 2011.
- Janet Urquhart (26 May 2011). "‘One-stop shopping for the Ice Age' near Snowmass". Aspen Times. Retrieved 5 July 2011.
- Snowmastodon Project FAQs. Denver Museum of Nature & Science and Snowmass Village, Colorado. March 11, 2011.
- "Snowmass Ground Score". AspenSpin.com. November 14, 2010. Retrieved July 8, 2011.
- "Discovery Timeline". Denver Museum of Nature & Science. Retrieved July 8, 2011.
- "First mammoth discovered in Snowmass gets new name". RealAspen. January 18, 2011. Retrieved July 8, 2011.
- "Snowmass fossil find continues to amaze". KDVR (Fox 31 Denver). June 3, 2011. Retrieved July 8, 2011.
- Jeff Pigati & Kirk Johnson (2011). "The Snowmastodon Site: Discovery, Science, and Initial Results". Newsletter of the Society (Colorado Scientific Society): 2. Retrieved July 11, 2011.
- Janet Urquhart (June 16, 2011). "Snowmass fossil dig yields bones at 'amazing rate'". The Aspen Times. Retrieved July 8, 2011.
- Marissa Lubeck (November 18, 2010). "Snowmass Fossil Site Provides Opportunity to Study Past Vegetation and Climate in Colorado". USGS Newsroom, U.S. Geological Survey. Retrieved July 11, 2011.
- John Stroud (July 2, 2011). "Area teachers diggin’ what they learned at Snowmass fossil site". Glenwood Springs Post Independent. Retrieved July 8, 2011.
- Electra Draper (November 19, 2010). "Denver museum staff euphoric over ice-age fossil finds". Denver Post. Retrieved July 8, 2011.
- "Museum reaches agreements to resume Snowmass fossil dig". The Aspen Times. May 11, 2011. Retrieved July 8, 2011.
- Kirk Johnson (July 7, 2011). "Museum Concludes Ice Age Fossil Excavation". Denver Museum of Nature & Science. Retrieved July 8, 2011.
- "Team Finds Evidence of Ice Age Horse". Denver Museum of Nature and Science. Retrieved 5 July 2011.
- Kirk Johnson (5 July 2011). "Pleistocene Treasures, at a Breakneck Pace". New York Times. Retrieved 5 July 2011.
- "Museum To Show Off Thousands Of Bones Unearthed Near Snowmass". CBS Denver. July 8, 2011. Retrieved July 11, 2011.
- Dennis Webb (June 5, 2011). "Snowmass fossil site continues to be ‘treasure trove’". The Daily Sentinel. Retrieved July 11, 2011.
- Troy Hooper (November 18, 2010). "Snowmass fossil site a 'once-in-a-lifetime' find". RealAspen. Retrieved July 11, 2011.
- Andrea Rael (June 10, 2011). "Snowmass Mastodon Project Coming To PBS With Support From National Geographic". The Huffington post. Retrieved July 11, 2011.
- "PBS Television Series Nova: Discovering Snowmastodon".
- Troy Hooper (July 11, 2011). "Significance of Snowmass fossil dig settles in as crews resume regularly scheduled construction project". Real Vail. Retrieved July 11, 2011.
- The Snowmastodon Project official website, Denver Museum of Nature & Science
- PBS Nova program on the Snowmass excavation project, broadcast February 1, 2012