National Geographic recently reported on the Red Desert to Hoback migration

Longest Land Mammal Migration in Lower 48 Discovered

"Deer are among the most ubiquitous animals in North America, giving humans ample chances to observe their habits. But until recently, scientists had missed one remarkable behavior of a hardy group of mule deer: a twice-yearly migration of 150 miles (240 kilometers), longer than any other land animal in the lower 48 states."

"In this great migration, several hundred deer travel across Wyoming, from a low desert to high mountains and back again. Their trek takes place outside the protection of any parks or preserves, and until now was done under the noses of the public. However, scientists warn that development and human intervention could threaten this ancient journey."