Passing is prohibited:

Passing is prohibited in a curve, on a hill, or in any other location where you would be unable to clearly see oncoming traffic. You may not pass within 100 feet of an intersection, bridge, viaduct, tunnel, underpass, or railroad crossing; when an approaching vehicle is in your passing lane; where signs or road markings prohibit passing; and when a vehicle ahead of you has stopped to let pedestrians cross the road.
DMV Writen Test