Burrows of the American Badger (Taxidea taxus)
Badgers are fossorial (adapted to life underground), digging burrows for den sites or to pursue prey such as pocket gophers. Their large fan-shaped mounds are impressive examples of bioturbation — soil disturbance caused by animals.
Whenever I encounter a badger mound, my eyebrows always seem to rise up in surprise. The volume of soil they displace is hard to believe. (For scale, my field notebook in the photos above is 5"x7".) Below the surface the burrows can be up to 30 feet long and 10 feet deep. The photos above were taken on 11 April 2012 (top two photos, same burrow from different angles) and 23 March 2012 (bottom photo).
Badgers have wide, low-slung bodies, and feet adapted for digging — long claws on the front feet and strong, broad hind feet for pushing soil backwards. I don't have a great picture of a badger yet, but here's one taken on Bodega Head in 2008.
To see a badger in action digging a burrow, check out this video posted on YouTube.