Patrick McGowan Jr. of Menifee, Calif., and Christopher Stasky of San Diego, both 42, died Thursday afternoon in a jump over Perris Valley Airport, The Desert Sun of Palm Springs reported.
Witnesses said their parachutes collided 200- to 300 feet in the air, deflating both of them. Neither skydiver was able to reinflate his chute.
The exact cause of the accident is unknown, pending further investigation by the Perris police, the Riverside County coroner, the National Transportation Safety Board and the Federal Aviation Administration.
People on the ground tried to administer CPR, but both men were pronounced dead at the scene.
"The two patients were in traumatic full arrest," the county fire department told the Los Angeles Times.
McGowan had been a skydiving instructor for Skydive Perris for nearly 20 years and oversaw parachuting at the airport, the Riverside Press-Enterprise reported. Stasky was helping him train parachute instructors for the Canadian military.
Scott Smith, western regional director of the U.S. Parachute Association, said McGowan had logged more than 17,000 jumps.