On May 6, 2003, about 1200 Pacific daylight time, a Cessna 152, N48796, collided with trees and terrain while practicing emergency procedures near Pala, California. Pinnacle Aviation Services, Inc., was operating the airplane under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) pilot and the private pilot under instruction (PUI) sustained minor injuries; the airplane was substantially damaged. The local instructional flight departed Carlsbad, California, about 1000. Day visual meteorological conditions prevailed, and no flight plan had been filed. The primary wreckage was at 33 degrees 23.0 minutes north latitude and 117 degrees 03.0 minutes west longitude. The CFI reported that the purpose of the flight was to practice emergency procedures. In the area of a rock quarry, they were performing a simulated engine out procedure. When the CFI called for a termination of the maneuver, he said that the PUI delayed in executing the proper go-around procedures. The PUI left the flaps at the 30-degree position, and the airspeed got slow enough to activate the stall warning horn. The CFI called for the flaps to 20 degrees and to "maintain airspeed." The CFI then called for flaps to 10 degrees, but the PUI mistakenly retracted them to 0 degrees. The airplane established a sink rate, and the CFI was unable to recover before the airplane impacted trees. The airplane came to rest approximately 50 yards from a dirt road. The airplane was destroyed during the impact sequence. Investigators from the Federal Aviation Administration examined the wreckage at the accident scene. They noted no pre-impact discrepancies with the airframe or the engine. The CFI and the PUI reported no mechanical malfunctions or failures with the airplane.