The tanker aircraft had taken off from Chico qualification check flight for pilots who were scheduled to conduct firefighting operations during the upcoming fire season. The accident flight involved conducting practice drops of water over an area of rugged mountainous terrain located north of the Chico Airport. Prior to departing on the flight, the airplane was loaded with 2,550 gallons of water. The Orion crashed and caught fire immediately following the training drop in the rugged terrain of the Lassen National Forest. PROBABLE CAUSE: “Terrain clearance was not maintained while maneuvering for undetermined reasons. Mountainous terrain was a factor.”