Copalis State, Copalis, WA (S16)
Correctly identified first by Dave Brown
Probably the only stretch of beach designated as an airport (at least in the Lower 48), Copalis State sits on a spectacular stretch of Olympic Peninsula coastline and has a runway that - when the tide is out - stretches up to 4500 feet north from the mouth of the Copalis River. Land on the damp sand - stay out of the dry sand (away from the surf line) or the real wet stuff right by the water's edge, both of which are very soft and will swallow your plane. When the tide is in, don't bother - the runway is under water. Watch out for wildlife, vehicles and/or pedestrians on the runway (and the lady who lives in the house just behind the high tide line who allegedly sometimes throws rocks at the airplanes landing on "her beach"). Who could ask for more?