In 1999, the jaw of a mammoth was collected from a gravel pit near Belgrade, Montana. During the Ice Age large continental glaciers originating from Canada covered the northern part of Montana. The glaciers blocked the path of the Missouri and Yellowstone Rivers and caused large glacial lakes to form. The sediments deposited in these lakes contain information on the climate and biological communities that lived in the region during the Ice Age. Excavations at Blacktail Cave Fossils from Blacktail Cave, located in northwestern Montana, date from about 40,000 to 10,000 years ago.
Animal remains found in the cave include many small mammals as well as bear and musk ox.
They provide a record of biotic change connected with the times before and after the last major glacial period. Glaciers of the Northern Rockies Glaciers covered the Rocky Mountains until about 12,000 years ago. They eroded the mountains, leaving scratches on the rocks and moving debris into the valleys. As the glaciers melted, the eroded sediments were left behind as piles of debris or deposited in streams. Small glaciers are still present in places like Glacier National Park and the Beartooth Mountains.