Acres of beach are covered with this at the Salton Sea, California.
You can find rocks made of these in the fossil record too and we call it the same thing, or sometimes “coquina” if it’s just 100% shells. It’s strange to see it being almost entirely barnacles like this though. There’s a fossil locality in Argentina near where I did my dissertation that has a couple thick intervals of pure barnacle hash like this, and it always stuck out as strange to me. It was obviously some kind of unusual event that caused the shells to all be barnacles with very little of the other shells that are usual for the area. Never did figure one out.
I was told that at one point the US Navy brought is some small ships for training on the waters there. The ships brought the barnacles. There are no natural predators for them there.
The water would rise, barnacles would start growing up to the new water mark. The water level falls, all of those barnacles die and smell really bad. There are old dead barnacle shells covering everything anywhere near the water. They are sharp and tear any bare feet right up. Not a cool place to go anymore.
I know this isn’t an answer to the image, but if anyone is interested, PBS produced a really great documentary about the Salton Sea and what contributed to things like this being all over the place. And the smell… Oh god, the smell… It’s called Plagues and Pleasures on the Salton Sea.