An East Bay Regional Park District police officer was shot at while on patrol near Moraga on Monday evening, police said.
Searches for the suspects ended unsuccessfully both Monday night and into Tuesday.
The officer was on foot patrol near the Upper San Leandro Reservoir at around 6:50 p.m. when two suspects fired an assault rifle at him.
Police said the officer returned fire and took cover. He was not injured in the attack.
The officer called for emergency assistance and was safely extricated from the scene using the park district police armored rescue vehicle, police said.
Police searched the area by foot and by helicopter until it grew too dark to continue. No suspects had been located as of early this morning.
Officers from the California Highway Patrol, the Contra Costa County Sheriff's Office, and the Richmond, Moraga, Orinda, and Lafayette police departments assisted in the search.
Police said they did not know why the suspects fired at the officer and the investigation is ongoing.
Anyone with information is asked to call police at (510) 881-1833.