This is one of the many beaver ponds along Grizzly Bear Trail. In several spots, the beaver ponds have swallowed the trail, requiring a detour and making you walk along the (often) precarious beaver dam in order to get to the other side. One such pond necessitated a lengthy detour and a bushwack over a ridge to reacquire the trail.
A section of South Dakota's 111 mile long Centennial Trail runs through the Black Elk Wilderness. The trails are quite scenic and fairly easy, though these are mountains and there is the usual up-and-down of mountain trails. Grizzly Bear Creek Trail as it approaches the Sylvan Lake/Harney Peak Trail is quite steep and also had many trees down across the trail when I was there.