The quick answer is that there was a volcano there, although I don't know how large it was. Cathedral Rock, which is due east of Mt. Daniel, is the remains of an ancient volcanic plug, so that entire subrange, consisting of Cathedral Rock, the Citadel, Mt. Daniel, and Mt. Hinman, are volcanic in nature. I don't think there was a huge mega-volcano like Mt. Rainier in the area, but it seems that this particular area had a volcano which went extinct and broke down into subpeaks much like the Goat Rocks Wilderness.