Marin County beach goers may want to reconsider their plans after a water main break closed a key access point between Highway 101 in Mill Valley and the road to Stinson Beach Saturday morning, the California Highway Patrol reported. Just after 9:30 a.m., the CHP put out an alert saying the exit ramp from northbound Highway 101 to State Route 1, which provides access to both Stinson Beach and Muir Woods, was closed as work crews dug up the pavement to access the broken pipe. The exit is the main route used to reach many parts of West Marin, always a popular weekend destination, and the CHP was cautioning drivers to avoid the area.