At about 1541 Mountain time, the airplane experienced a total loss of engine power while cruising. The pilot diverted to the nearest airport but was forced to land in an open field. The airplane nosed over during rollout and was substantially damaged. The commercial pilot and passenger sustained minor injuries. Visual conditions prevailed. According to the pilot, he departed Boise with a total of 89 gallons of fuel. Upon landing in Pocatello, 57 gallons of fuel remained. Prior to departing for the return to Boise, he added 20 gallons of fuel to the airplane. Only about two gallons of fuel were found in the tanks.