I was able to get in an impromptu mud session at a place I wanted to check out in Indiana while on the way back from vacation. Here is a short clip at the end. I will try to post a longer clip later, though it's not one of the better spots I've visited. There was a lot of thin mud on top, but most of the thicker areas and down deep was mostly sand. Still fun, but this place definitely put the sand in sand and gravel. It's too bad because (at least when I visited) it had a greate cleanup spot with water pouring gently out of a pipe into some sand/light gravel, then draining to another pipe. Basically made for an outdoor shower. No head coverage as I still had a 5 hour drive back and didn't want to both with that.
Hope you enjoy.