On Sept. 2, 1994, a heavy equipment operator for Prairie Land and Timber discovered a large bone while digging in Tolo Lake, and the four-foot-long, twelve-inch-diameter bone proved to be the thigh bone of a Columbian mammoth, Mammuthus Columbia. In one summer of excavating, bones from at least nine mammoths and two prehistoric bison, Bison antiques, were uncovered in Tolo Lake. Scientists believe Tolo Lake may be the largest mammoth graveyard in the United States, with up to 200 mammoth skeletons. The excavation was led by Idaho Museum of Natural History staff in cooperation with the Idaho State Historical Society and the University of Idaho, with volunteers from Grangeville and as far away as Tennessee assisting with excavation, tours, and support. Tolo Lake received almost 12,000 visitors for site tours during the summer of 1995. Tolo Lake lies about five miles west of Grangeville on the edge of the Camas Prairie, and the discovery resulted from work intended to improve fish and wildlife habitat and recreational opportunities at the lake. The bones and excavation site have been covered with 86 million gallons of water to protect them from weathering and disturbance, while the Idaho Museum of Natural History retains the option to continue excavation if funding becomes available.