The San Mateo campground is next to Camp Pendleton Marine base in San Clemente, California, and is part of San Onofre State Beach. It’s an attractive campground with lots of room between sites. There is a scenic 1.5 mile nature trail that connects the campground to Trestles Beach. A creek, San Mateo Creek, is just east of the campground and goes all the way to the ocean. It has created a wetland habitat for lots of critters, some of which are rare and/or endangered.