At approximately 16:10 mountain time, a Piper PA-28-181 struck terrain while maneuvering about 20 miles west of Sheridan. The pilot was not injured, but his passenger sustained a serious injury. The pilot was flying IFR from Pierre, S.D., to Red Lodge, Mont. West of Sheridan, he cancelled his IFR flight plan and received VFR flight following as he started crossing the Big Horn Mountains. He turned up a valley and soon realized the terrain was rising faster than the airplane could climb. Terrain proximity precluded him from turning around, so he elected to land in a meadow. Both wings and the fuselage were buckled.