The Florissant Fossil Formation is a lagerstätte in the Colarado part of the Rocky Mountains. It shows life in the Eocene in as-yet unraised part of what is now the Rocky Mountains. It shows the whole forest ecosystem in some detail, particularly the plants. From this we can be sure the forest was sub-tropical, and the climate much warmer than today.
- Meyer, Herbert W. 2003. The fossils of Florissant. Smithsonian, Philadelphia. ISBN 1-58834-107-0