The two aircraft collided in flight approximately three miles south of the Gillespie Field Airport at 1642 Pacific time. Both aircraft were destroyed in the collision sequence and post-impact fires. The CFI and pilot undergoing instruction in the Cessna 172RG and the Private pilot/sole occupant of the Cessna 182Q were fatally injured. Visual conditions prevailed, and included high broken cloud cover with a visibility of 25 miles. A pilot-rated witness reported the two airplanes were flying at an estimated 1800 feet msl. One airplane was flying southwest; the other was flying east. The airplanes were in the Gillespie Field Class Delta airspace when the airplane flying eastbound impacted the airplane flying southwest bound. The eastbound airplane impacted the right side of the southwest-bound airplane. Upon impact there was a ball of fire and the wings separated from the fuselages of the airplanes as they descended to the ground. The distance between the impact point of the main wreckages of the Cessna 172RG and the Cessna 182Q was about 810 feet. The wings of the Cessna 172RG came to rest approximately 430 feet from each other. The Cessna 182Qs right wing was located 1000 feet north-northeast of the main wreckage. Its left wing was approximately 775 feet northwest of the main wreckage and near the locations of the Cessna 172RG wings. Investigators located the Cessna 182Qs left aileron between the left wing of the Cessna 182Q and the left wing of the Cessna 172.