Solved! This is Kew Gardens Parkway on Long Island, NY. Of Robert Moses provenance. I love misplaced optimisim of the forelorn sidewalk and lone bench, as if anyone would actually walk there. Thanks to an eagle-eyed user on Dead Memories Portland!
Amongst some of the slides are others of unknown origin.
Not even sure if this is Portland but figure if it is, it must be McLoughlin Blvd.