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Police are warning those who use the Iron Horse Trail between Walnut Creek and Concord to be on the lookout for this man, who they say has flashed at least six people on the trail since March 19. (Walnut Creek Police Department)

Police are warning those who use the Iron Horse Trail between Walnut Creek and Concord to be alert after the latest in a series of reported flashings by a man on the trail.

East Bay Regional Park District police released a sketch of a man suspected in the June 5 flashing of a woman on the trail, Lt. Jon King said. That incident was the sixth on the trail since March 19.

All of the flashings have occurred between Treat Boulevard and Lincoln Avenue, located south of the Walnut Creek Library, and all have occurred in the late afternoon or early evening, King said.

The time of the incidents "is the only common thread," King said. "So far, there's been no violence involved. It's just a matter of a man exposing himself."

The suspected flasher was described by police as a white male with dirty blond, shoulder-length hair. He is approximately 5 feet 10 inches tall with a thin build and has been reported to be walking or riding on a BMX bicycle when the incidents have occurred, King said. He also has been reported to be wearing a baseball cap.

While the flasher hasn't been violent, that doesn't mean he's not dangerous, King added.

"It's always a concern that eventually the actions will escalate," he said. "The advice to people on the trail would be the same as it always would be. It's always best to go with friends, and to be aware of your surroundings. People walk with earphones now, but it's best to keep one of those earphones out so you can hear what's going on around you."

Walnut Creek police and the Contra Costa Sheriff's Office also are working with the regional park police on the investigation, King said. Anyone who sees the man is urged to call 911 or East Bay Regional Park police at 510-881-1833.

Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.