Geograph - photograph every grid square

There was an opencast coal mine operating South of here between 2012 and 2016, but this structure obviously easily predates that. I'm guessing it was built to get the mud off forestry vehicles (trees were here before the modern mine and were replanted when it closed) before they exited onto the main road a few decades ago, but with there being no online mapping available between the early 1960s and now it is hard to know for sure.
The low wall on the left indicates the position of the wheel bath. Be careful if walking on the grassy bit - some of the metal sections have a tendency to move down too much for comfort in the middle!