Authorities were searching Friday for a motorist suspected in a hit-and-run crash on Pine Flat Road near Highway 128 in Alexander Valley that left a bicyclist gravely injured.

Few details about the bicyclist, including his name, were immediately available. He was airlifted to Santa Rosa Memorial Hospital at 1:35 p.m., unconscious with major head injuries, the CHP said.

It was the latest in a series of vehicle-versus-bicyclist incidents that have left three dead in a month.

The Sonoma County Sheriff's Office put out a be-on-the-lookout bulletin for a 1990s model black sedan with blood on its windshield, the CHP said. The Sheriff's Office on Friday night could provide no additional information.

CHP Officer Mike Brown said that what is known so far is that the bicyclist was headed downhill at a high rate of speed when he collided with a car traveling uphill.

On June 19, retired SSU professor Steve Norwick, 68, died. He had been struck on his bicycle by a hit-and-run driver on Petaluma Hill Road. Robert Cowart, 68, of Penngrove, has been charged in that case.

Two other men have died since May 24 in vehicle-versus-bicycle accidents in the county.