The steel grates that you see in the front stop any large sticks or trees from coming in which is perfect because it also makes the mud just mud and nothing else
It's an old water pump house that used to be used for a concrete plant. There's many of these old pump houses that run through Hagerstown Maryland along this Creek. They also have water screens in them that take all of the nastiness out that's why the mud is almost perfectly pure clay and river silt.
Hey I was going through my old posts and just noticed you asked where in hagerstown md my two mudpits are. If you'd still like to know just shoot me a message in here I'd be happy to give anyone the location.