No, it isn’t Bigfoot, it is not a wolverine, a rabbit or even a cat (although these were all good guesses.) It is in fact a fox that was introduced to San Juan Island.
The person who solved the puzzle is “Anonymous,” who, as it turns out, lives in the heart of the Silicon Valley, but was somehow able to solve the mystery (how on earth did you figure it out??) Anyhow, Anonymous has contacted me and will get a Cactus Eaters-related one-of-a-kind handmade prize (providing that she agrees not to sell the prize on eBay later on.) Above are two full pictures of the spooky, and now fully identified, critter (one is the actual photograph, and the other is an artistic recreation.)
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