When in Gerryowen, we also visited Yellowtail Dam and Pompeys Pillar.
Yellowtail Dam is on the Bighorn River and on the list of little known but you should see National Recreation Areas. It is beautiful!
We also visited Pompeys Pillar National Monument. Not nearly as impressive as Devils Tower but a nice chunk of rock located right next to the Yellowstone River. Also considered sacred by the Native Americans. The name Pompeys Pillar came about because William Clark and Sacajawea along with her son, nicknamed Pomp by Clark, stopped in the area and Clark named the rock after Pomp. Clarks signature also graces the rock.