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 on having the glider towed to 4,000 feet above ground level (agl), which would be 5,600 feet msl, then release the tow line. During the tow, the pilot released from the tow plane when the altimeter read 4,000 feet. 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 forced landing 2 miles short of the runway into desert terrain. 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.