On August 16, 2000, about 0715 hours Pacific daylight time, a Schweizer G-164B, N6543R, sustained substantial damage when it nosed over during a forced landing on a dirt road near Olancha, California. The forced landing was precipitated by a loss of engine power during cruise. San Joaquin Helicopters, Inc., operated the airplane under the provisions of 14 CFR Part 91. The commercial pilot sustained minor injuries. The positioning flight departed Delano, California, about 0550, and was en route to Lone Pine, California, where it was to be refueled and loaded with chemicals for aerial application work. Visual meteorological conditions prevailed and no flight plan had been filed. The pilot told a responding sheriff's deputy the engine lost power and he attempted to land on a dirt road. The roadbed was lower than the dirt shoulders. The lower left wing dug into the shoulder and the airplane nosed over. The pilot thought the airplane might be out of fuel. The deputy did not observe fuel leaking on the ground or any wet spots under the inverted airplane. The operator said the airplane had a main fuel tank containing 48 gallons and an auxiliary 17-gallon tank. The Federal Aviation Administration accident coordinator observed the operator recover the airplane. After the airplane was righted during recovery, he noted that recovery personnel drained 3 gallons of fuel from the fuel system. The operator said this represented the unusable fuel quantity for this airplane. In his written statement, the pilot said there was no mechanical malfunction of the airplane or engine.