Looks like an overnight dusting at some of the places around me. As I said, drifts can be deep, but snowfall like that pictured is uncommon in the Great Plains (probably why that image has lasted as long as it has). As far as the animals you mentioned, those are most likely relic populations. And I was probably simplistic when I talked about migration; bison will move to areas that provide better thermal cover during the winter - that may be downslope, or even north if conditions are more favorable.
I'm sure the manner in which the snow gets deep is very meaningful to the animal.
As far as the animals you mentioned, those are most likely relic populations.
Most likely. Relics aren't affected by the weather.
...bison will move to areas that provide better thermal cover during the winter - that may be downslope, or even north if conditions are more favorable.
Undoubtedly how the American Bison got its reputation for being able to withstand the worst imaginable winter conditions.