Right. So. This morning, whilst gettin' right on that good Starbucks iced coffee and putting together the blog post about Mound Key, I typed "Mound Key, FL" into ye old Google Maps and got the image you see above.
Only after I'd copied it and prepared to add it to the article did I realize it wasn't Mound Key. Evidently Google had a hiccup or something, and deposited me in parts unknown. I even went back into my browser history, and when I clicked the link to the hiccuped map, it brought me to the proper location this time. So now I'm going half-mad, three-quarters mad, even, trying to figure out where the heck this place in the mystery photo is. It looks very much like the same terrain as the vicinity of Mound Key - South-Gulf-style swampland - but I couldn't find it again. So help me, Obi-Wan Internet, you're my only hope. If you're able to re-find this spot for me, I'll reward you with cake or something.
The really maddening thing is, I was all excited when I thought this was Mound Key, because the surface features seem to show a deliberate effort to create an image of a crustacean, or possibly a pineapple, much in the same manner of the animals depicted in the famous Nazca Plain. But I can't research further until I know where this place is.
Update! You see, the Internet really is good for something! Within half an hour of posting this, the ever-resourceful @betsylayne solved the mystery - apparently there's a Big Mound Key in addition to regular original-recipe Mound Key, and the crablike structure is located just south of Boggess Hole.