An armored crossing are stream crossings that have been "armored" with rocks to protect the stream bed and to keep out of the mud. I've always been leery of those, and on this trail in particular they are either in a curve or not far from a switchback.

Your description of skidding out on the curve that way makes me remember when I skidded in the dust a few weeks back when I tweaked my bad knee. I bet that is what happened...