NOAA states a 100 yard distance from beached seals and sea lions. http://www.westcoast.fisheries.noaa.gov/publications/protected_species/marine_mammals/pinnipeds/casealviewbrochure.pdf
Note for photographers: These were viewed from above. A long lens and shooting from a distance gives a shallower angle. Fortunately this beach was roped off and there are docents there to help protect the marine mammals. This particular beach used to be a children's swimming beach and is a big point of controversy in La Jolla. The beach is closed in breeding season.
All images © Kim Moore (contact for use)