Three stories. Yeah... a few friends and a shovel. lol
That appears to be a retaining wall and everything uphill is following the path of least resistance. Hose. Pressure wash. Dehumidify. Ultraviolet light. Nude dancers. That wall is not a quick fix.
This past "winter" in Los Angeles was laughable. It was dry with the exception of a couple downpours. I mean, it's going to be 90 in LA today.
I'd clean up the floor... hose and brush ot off (it looks like ****************) and would consider some 2x4 framing and some half-inch plywood... so you don't get your yeezers dirty.
