Brown coal from five mines on the Red Desert in Central Wyoming has been studied for plant microfossils. These suggest an Eocene vegetation similar to that now present in the Southeastern United States and a climate similar to it.
Proceedings of the Iowa Academy of Science
©1941 Iowa Academy of Science, Inc.
Wilson, L. R. and Webster, R. M.
"The Eocene Vegetation of the Red Desert in Wyoming (Abstract),"
Proceedings of the Iowa Academy of Science, 48(1), 198-198.
Available at: https://scholarworks.uni.edu/pias/vol48/iss1/35