This is an American Three-toed Woodpecker (Picoides dorsalis). It's a fairly unusual sight this far out on the plains. From All About Birds we see that it prefers "...boreal forests and montane coniferous forests across North America. Because of its choice of habitat, it is infrequently seen by most people."
It resembles, and is therefore sometimes confused with, the Black-backed Woodpecker. The two species often co-exist in the same habitat.
Both species are quite fond of wood-boring beetles, which would tend to explain the attraction of The Smile Hi's elm trees these days.