Take a walk by the old irrigation pond and look for migrating waterfowl, like buffleheads, coots, mergansers and grebes. Take some time to go down to Cove Beach, a nice place to enjoy a snack, read a book or relax. Sometimes the younger, less aggressive bulls will come ashore to find respite from the competition of the breeding colony. I've even seen dead animals wash ashore here with shark bites, and although gruesome to contemplate, they are an incredible sight. Pescadero Marsh has excellent birding.
Many beaches have excellent tide pools.
Bring your mountain bike to Wilder Ranch State Park or Big Basin State Park.