"Salt chuck" in a surprising place

[David D. Robertson]

I find it surprising to see a current nationally-published guidebook, the
American Austomobile Association (AAA) "Campbook" for the Northwest states,
including a description of a campground in Washington's San Juan Islands as
having a "salt chuck".  No one but a few geeks (sorry) on this list & a few
old-timers from the Pacific NW would understand that term, right?