I looked it up as a possible stop on the way down Mex1, appears to be a typical park of this area, fenced, gated, beach-less and faceless. Here it is on the old page of On the Road In (you won't find it in new page):
Clam Beach.
Note the open gate and empty security booth. Also typical for many parks - they only man the booth on weekends. Scroll down for more photos. It says "on the ocean" but doesn't show any beach, and I suspect that like many other parks in the area, it has no beach - only embankment with boulders. There are probably better photos on Google Earth.
Very few parks with "beach" in the name actually have a beach, and there are definitely no clams.
Eventually decided to stop past Ensenada in a camp called Mona Lisa. A bit cheaper than neighboring Estero Beach. Needless to remind about negotiating a price in small owner-operated parks in Mexico (not sure that Clam falls in this category).
Ask at Baja Nomads forum maybe.