Denver ? The Rocky Mountain Ice Age is slowly making a comeback in Colorado as scientists begin to analyze an estimated 600 fossils and hundreds of pounds of plant matter unearthed near a ski town.

The findings from the one site in western Colorado are “once-in-a-lifetime” discoveries, said Kirk Johnson, chief curator and vice president for research and collections at the Denver Museum of Nature and Science.

“This is our first clear window into the Ice Age” in Colorado, Johnson said Thursday at the museum. He was speaking to a packed room with reporters, visitors, and a row of children a few feet from a table with parts of the remains of mastodons, mammoths, and a piece of the first ever ground sloth ever found in the state. It’s also the highest-altitude ground sloth ever found in North America, museum officials said.

Johnson said the discoveries are unique because they all came from the same dig site near the town of Snowmass Village. Other times, scientists only find the remains of a single animal at one site, he said.

The discoveries were set in motion on Oct. 14, when a man operating a bulldozer to expand a reservoir near the town ran over a fossil. Johnson credits’ the keen eye of the bulldozer operator for spotting the fossil.

“Some people say, ‘Oh, it’s a bone, bulldoze it!’ ” Johnson said. Instead, the worker, Jesse Steele, and a colleague checked online to try to figure what the bone was and called the museum. The fossil turned out to be the remains of a Columbian mammoth.

Museum workers began digging at the site Nov. 2 and what they found was staggering. So far, the discoveries include the remains of as many as 10 American mastodons, four Columbian mammoths, four Ice Age bison, the ground sloth, and many Ice Age insects. They’ve also found pieces of chewed wood that show evidence of Ice Age beavers, and large amounts of well-preserved wood, seeds, and other plans.

Work at the site is finished for the winter but the museum wants to return next year when snow melts.

“Stay tuned for the spring,” said Ian Miler, the museum’s curator of paleontology and chair of the Earth Science Department.

Colorado scientists are already saying the discoveries at the dig site are among the most important in Colorado history.

U.S. Geological Survey scientists say lab results from the site show it could be as old as 130,000 years old. The geologists said in a statement it appears the fossils were “deposited in a small lake or marsh that formed when a stream was dammed by a glacial moraine, or accumulation of glacier debris.”

The geologists said the discoveries from the dig site have provided them “with more than 100,000 years of vegetation and climate records in Colorado.”

“It’s hard to describe what a stunningly thrilling month this has been,” said George Sparks, the president and CEO of the museum.