"Belfair State Park on scenic Hood Canal. One of Washington's many parks which provides camping, swimming, picnicking and relaxation for all who visit 'Belfair-by-the-Sea.'"
Both of those Pontiac GTOs in there look vintage 1965-1967 to me (click on image to enlarge). Note the lack of any self-contained motor homes. Around here at least they were not really in abundance until the 1970s. Before that time we saw more campers on pickup trucks and towable trailers.