These photos were taken at Ft. Niobrara NWR. The prairie dog town is the first stop on the auto tour of the refuge. Quoting from the auto tour pamphlet:
On both sides of the road the dirt mounds of a small prairie dog town can be seen. The most widespread of the five species in North America, the black tailed prairie dog, is found in Nebraska and across North America from Canada to Mexico. This town, just as yours, has neighbors called "wards" and family groups called "coteries". Each coterie usually consists of a single adult male, one to four adult females, and any of their offspring less than two years old. Each group defends a territory of about one acre, greeting its own members with a "kiss" and challenging any intruders to a fight. Coyotes, eagles, hawks, owls, rattlesnakes, badgers, and weasels hunt here. The small Burrowing owls also find a home here in an abandoned hole where they lay their eggs and raise their young. Look for them perched on a mound or making low short flights in the town.