Two riders killed in a crash near Palomar Mountain on Sunday afternoon died in a head-on collision after one rider veered into the oncoming lane and struck another rider, authorities said. The deadly collision was reported around 1:25 p.m. on East Grade Road near mile marker 10.6, east of  Crestline Road, California Highway Patrol Officer Hunter Gerber said Monday. According to the CHP,  a 68-year-old Fallbrook man was riding up the mountain in the eastbound lane on his Harley-Davidson motorcycle when for unknown reasons he veered into oncoming traffic. He ran into a Yamaha motorcycle ridden by a 71-year-old Escondido resident who was heading west or downhill, the CHP said. Both men died before they could be taken to a hospital. The names of the riders were not immediately released. Alcohol and or drugs do not appear to be a factor in the crash, Gerber said. The incident remains under investigation. Anyone with information or video of the incident is asked to contact the CHP Oceanside office at (760) 643-3400.