Buried Treasures

How Snowmass Village became the improbable—and mysterious—site of a fossil mother lode that may redefine Colorado’s evolutionary history.

May 2011

Last October, Kirk Johnson got the call: A bulldozer driver named Jesse Steele had unearthed ribs, vertebrae, and a tusk belonging to a young, female Colombian mammoth while excavating a dam at Ziegler Reservoir near the Snowmass Village ski resort. Johnson, curator and vice president for research and collections at the Denver Museum of Nature and Science, felt the familiar excitement. For the career paleontologist and geologist, mammoth discoveries are not unusual, with at least partial remains surfacing every several years. The finds are wonderful, but, Johnson says, “When a construction worker calls me up and says, ‘I think I found a mammoth bone,’ I say, ‘Yeah, you probably did.’ ”

Still, each discovery demands investigation, so the next day, he dispatched a crew to plan for further exploration in Snowmass. About 10 days later, Johnson visited the site himself, along with colleagues Steven Holen and Ian Miller. Expecting little more than the usual handful of bones, the three researchers didn’t even bring tools.

They laid out what had been found inside a building at the reservoir. As they examined the remains, Holen noticed another mammoth leg bone, clearly from a larger specimen. From that moment, nothing about the dig would be routine.

Most Ice Age sites yield one animal; finding two is rare. The Ziegler site went from rare to one-of-a-kind before Holen could put down the second bone. While Johnson and his peers were still mulling the magnitude of the dual find, a bulldozer unearthed a third leg bone in a different part of the reservoir.

A few days later, the three men returned to Denver, still abuzz from the excitement of the unique find. The next morning, workers in charge of excavating the reservoir uncovered more tusks and a tooth. One of them took a photo of the tooth and sent it to Johnson, who saw immediately it wasn’t from one of the mammoths. This tooth belonged to a mastodon, and it sparked a frenzy of questions about what on earth had happened at Ziegler.

In 2009, when two boys digging in the dirt near Ken-Caryl Ranch unearthed a partial jawbone and tusk, it was hailed as the most significant mastodon find in Colorado. Remains from the ancient elephantine creatures are littered throughout North America, from Alaska to Honduras, but they’ve almost never been found in Colorado; the Ken-Caryl bones were only the third discovery of mastodon fossils in the state. At the time, Holen told the Denver Post it was “the first good record of an American mastodon in Colorado.”

Nestled high in the mountains outside of Aspen, however, the Ziegler find showed that mastodons have a far more expansive history in Colorado than anyone had realized. Within a few weeks of the discovery, the museum had installed a crew at the site while construction workers excavated the dam, carefully avoiding what they thought was a single site. By the start of ski season (and the end of digging season) several weeks later, museum crews would identify 28 different piles of fossils at Ziegler, yielding almost 600 bones from as many as 10 individual mastodons—including 16 tusks and the first mastodon skull ever unearthed in Colorado. Some of Ziegler’s skeletons are more than 50 percent complete, and not all the bones are from the prehistoric proboscideans. The ancient lake is teeming with fossils: The remains of at least five species of large Ice Age animals are preserved at Ziegler, including a Jefferson’s ground sloth the size of an ox, a small deer-like animal, and several huge Ice Age bison with horns spanning six feet across.