Back in May 2019 I posted here on the Twin Islands. They don’t appear on all maps, but they are on this one of Providence…
At that time I was unable to find an actual photo of them. The photo is now found, and it also looks like it has a date that more or less fits…
The cameraman was up on Fort Hill and the picture looks up the Seekonk which then curves around to the left and goes out of sight. As a strong lad Lovecraft was a keen rower in a boat on the Seekonk, and he went down past the bridge and landed on these islands…
I used to row considerably on the Seekonk … Often I would land on one or both of the Twin Islands — for islands (associated with remote secrets, pirate treasure, and all that) always fascinated me.” — Lovecraft letter to Rimel, April 1934.
Being rather tidal, presumably they had a quite Dagon-ish texture underfoot…
When at last I awaked, it was to discover myself half sucked into a slimy expanse of hellish black mire which extended about me in monotonous undulations as far as I could see, and in which my boat lay grounded some distance away. — “Dagon