At about 2100 Central time, the airplane was substantially damaged during an emergency landing on Runway 21 at the Bismarck Municipal Airport (BIS) in Bismarck, N.D. The right main landing gear failed to extend prior to landing and the left main gear collapsed during rollout. The airplane subsequently departed the runway pavement before coming to rest. Visual conditions prevailed, and neither the Private pilot nor the passenger reported injuries. The pilot elected to divert to BIS when the landing failed to extend prior to landing at his intended destination.