The glider pilot stated that he set the altimeter to the field elevation of 1,600 feet mean sea level (msl) before takeoff. He planned to have the glider towed to 4,000 feet above ground level (agl), which would be 5,600 feet msl, then to release the tow line. During the tow, the pilot released from the tow plane when the altimeter read 4,000 feet (which was 2,400 feet agl). During the return glide back to the airport in a headwind, he realized he was too low to make it to the airport and executed a landing 2 miles short of the runway into desert terrain. On final approach for landing, the pilot maneuvered the glider to avoid a canal. The glider landed hard, and the fuselage sustained substantial damage. The pilot stated that he mistakenly released from the tow at 4,000 feet msl, when he should have released at 4,000 feet agl. He also stated that the glider had no mechanical failures or malfunctions during the flight.