Ano Nuevo State Park
Admission: $7 (for guided tours) and $10 for parking (per car)
Ano Nuevo State Park is probably the best place in all of California (if not the world) to check out elephant seals in their natural habitat. The seals are usually out on the beach at any given time, but maybe be there for different reasons (fighting for mates, birthing, molting, etc.) depending on the time of the year.
During the breeding and birthing season, the beaches are only accessible by guided tour to prevent idiots from getting too close to the seals.