(07-26) 13:01 PDT MORAGA --

An East Bay Regional Park District police SWAT team launched an intensive search of heavily wooded terrain near Moraga today, the morning after a gunman who was probably protecting a marijuana-growing operation fired at an officer with a rifle, authorities said.

The district's special response unit was searching a remote area near Upper San Leandro Reservoir and Rancho Laguna Park south of Moraga for any signs of the assailant.

At least one gunman fired shots from a rifle at a park district officer on patrol at 7 p.m. Monday. The officer was not injured and called for emergency backup.

The district's SWAT team and officers from other agencies brought him to safety. A multi-agency manhunt Monday evening that included helicopters from the park district and the California Highway Patrol turned up nothing.

Today, the SWAT team returned to the area to look for the shooter. Authorities believe he was protecting a pot-growing operation, which are often found in remote park lands.

"The officer was shot at with rifle fire, so we don't take these things lightly," park district police Capt. Mark Ruppenthal told reporters.