Marc, you nailed it! It’s located in Washington DC at the National Gallery of Art Sculpture Garden. This piece is at the NW corner of Constitution Ave NW and 9th St NW. I’m sure many (young) people are perplexed by it.
Try as I might to think of something else... is this a huge version of one of those old-school disc erasers with the brush attachment? And... if so... where the heck it his?? LOL!