Each day brings new surprises for scientists who are digging at the bottom of Ziegler Reservoir in Snowmass. Monday they uncovered a second mammoth. And over the weekend, they pulled the skull and horns of a gigantic Ice Age bison from the muddy silt.  This unfolding discovery started in mid-October when a construction worker uncovered the bones of the first Columbian mammoth. Since then, researchers have found bones from what they believe are five mastodons and several other mammals. Kirk Johnson is the chief curator at the Denver Museum of Nature and Science. (Photo by Heather Russo)