SNOWMASS VILLAGE - The bone count at Ziegler Reservoir near Snowmass Village stood at 2,863 on Wednesday morning. The tally likely wasn't accurate for long."We have been digging bones at a pretty amazing rate," said Dr. Kirk Johnson, chief curator at the Denver Museum of Nature & Science and one of the leaders of the dig, leading a media tour. "The site has continued to produce at extraordinary rates."By that, Johnson meant 301 bones recovered on Tuesday - the biggest day yet at the dig.After weeks of toiling in poor weather and deep mud, the museum's rotating crew of volunteers at Ziegler is working in dry, pleasant conditions these days, and making steady progress. Big machinery moves piles of dirt once it's overturned by the ever-watchful shovel crew, which has reached the bottom of the glacial lake, a bowl carved out of a ridge just west of the present-day resort during the last Ice Age.They need go no deeper. All of the fossils, which scientists believe are between 50,000 and 150,000 years old, lie in the layers above the glacial till at the lake bottom, Johnson explained."We're just scraping the frosting off the bowl," he said. "Once we've scraped off all of the frosting from the bowl, we're done."The effort is concentrated at the end of the reservoir where construction of a dam will begin early next month. The goal, Johnson said, is to prevent the destruction of any fossils with the building of the dam, and the fossil recovery is on schedule."The end of the job is in sight," he said.Whatever remains buried in the rest of the reservoir - and there is likely more to be found - will be "archived" for future exploration, he said. The remaining fossils aren't going anywhere except back under water, Johnson has said previously. Still buried, they remain protected.Starting Thursday, the main force of outside scientists summoned to Ziegler will begin arriving. In all, 37 experts from 18 universities will be involved, according to Johnson; 27 of them will be at Ziegler next week, he said.Specialists will try to date the various layers of the lake and collect pollen grains that will yield clues to climate and vegetation, among other endeavors. Still to be determined is why so many animals are congregated there. The data analysis will require another one to two years, but the goal is piecing together a picture of an alpine lake that predates the presence of humans, Johnson said."This is a pristine, pre-human ecosystem," he said. "What we're sampling is a lost world of ancient Colorado."It's probably the best, high-elevation Ice Age site in North America, if not the world."Huge mastodon tusks and other bones continue to surface at Ziegler, which could become the top-producing site for mastodon fossils in North America before it's all over, according to Johnson. The second-most common bones have come from bison; bones from the Jefferson's ground sloth are third. Very little had ever been recovered in Colorado of either mastodons or sloths before Ziegler.The complete skull of a sloth - "an amazing fossil," Johnson said - was uncovered this week. It was encased in burlap and plaster immediately - a way to protect the larger bones for their transport to the museum in Denver.No evidence of a large carnivore has yet been discovered, but Johnson is offering $500 to the dig-crew member who unearths the skull of a short-faced bear.The first bone of an Ice Age species of horse was exhumed last weekend, and Johnson expects the list to grow as the expanding collection of fossils is examined closely in Denver."I'm quite certain that new species have slipped past us," he said.A partial tally of what's been discovered so far includes the bones of mastodons, Columbian mammoths, sloth, bison, deer, camel, horse and a variety of small critters such as snakes, fish, salamanders and rodents.A thick layer of peat scraped off the lake contained intact plant matter (a pile of it is available at the Rodeo Lot in Snowmass for anyone looking to give their garden an Ice Age boost) and the dig crew has uncovered larger pieces of wood, as well."This piece of wood is five times older than civilization," the charismatic Johnson exclaimed Wednesday, hoisting a piece that, as he put it, is so well-preserved, it looks like it came from a tree that died in someone's back yard last year.