@littlerachyb very nice thread, it looks wild down there. I've not heard of 'tinners pits' are they left over from small scale tin ore mining?
We have 'borrow pits' up here, really small scale quarries, where stone was won to provide the materials for farmhouses, dry stone walls, etc. They still get used occasionally to make forestry roads or access roads to wind farms.
Hope you enjoyed your walk, lots going on there!