You can cut to the chase by going to the award winning video, I'd recommend full screen mode.
I never thought mule deer migrated other than elevation changes to get out of the deep snow. That's been the conventional wisdom as far as I could remember. Recently some scientists doing research on muleys down in the Red Desert made this amazing discovery.
The Red Desert is roughly the area between Rawlins and Rock Springs. In Wyoming north of the Utah/Colorado/Wyoming border. It's a little lower than the surrounding sage brush and the topography offers some shelter from the fierce winter winds.
In the spring the deer migrate up across the flats by I-80 then North and West hugging the West side of the Wind River Range before finally breaking up and dispersing into the Gros Ventre "Grow Vonts" and the northern portions of the Wyoming Range all the way to Hoback Junction. That height of land where the Hobacks meet the Gros Ventre, seems to be the extent of it, they don't go into the Snake River Valley or Jackson Hole or anything.
A hundred and fifty miles is a long way to go.
This is the longest migration of a large mammal in the lower 48.
I've been watching mule deer every day for a couple of weeks now. I'm working in what's called the "urban wildlands interface" or some kind of gobledeegook. It means commuters living in unlandscaped mountainous places with a high density of houses. Unlike the deer I see, the deer in this video are 100% wild.
I'd call the deer where I work, semi wild. They live amongst widely spaced houses often eating off irrigated ornamental plantings while attempting to get some relief from the constant predation of one of the densest mountain lion populations in the Rocky Mountains. The deer in the video live in some of the most uninhabited places in the lower 48 and populations are thought to be in decline.
I like the wild deer very much and for me they have great value as does the desolate landscape of south western Wyoming.