In Playa Del Rey, California I usually go out to the jetty and look down around the rocks especially at low tide to find these birds. They will tend to rest at high tide and forage mostly near low tide, so they can easily get food.
Their diet consists mostly of mussels, limpets and other shellfish. Occasionally will eat whelks, urchins, and crabs. When they eat a mussel, they will remove the mussel from its shell and leave the shell in place still in the mussel beds. The Oyestercatcher will either quickly jab its bill into a slightly open mussel shell cutting the muscle, then eating the contents. The other way they eat muscles, is to hammer on the shell with their bill until it breaks open.
They can be found all seasons along rock shorelines from Alaska to Baja. Will choose areas with abundant shellfish, not many can be found along the coast of Southern California since the shoreline is very sandy.