On February 3, 2005, about 1330 Pacific standard time, a Cessna 172M, N472RA, collided with terrain during an off airport, soft field landing near Desert Center, California. Stang-Air was operating the airplane under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) and pilot undergoing instruction (PUI) were not injured; the airplane sustained substantial damage. The personal cross-country flight departed Brackett Field Airport, La Verne, California, about 1300, with the planned destination of Ernest A. Love Field Airport, Prescott, Arizona. Visual meteorological conditions prevailed, and a flight plan had not been filed. In a statement to the National Transportation Safety Board investigator in-charge (IIC), the CFI reported that while in cruise flight, he decided to demonstrate an off airport, soft field landing on a dry lakebed. The CFI had not previously planned to land on the dry lakebed and had no information as to the condition of the landing surface. The landing surface was softer than the CFI anticipated. During the touchdown, the main landing gear sank into the sand, and the airplane nosed over. The CFI stated that the airplane and engine had no mechanical failures or malfunctions during the flight.