Thin layer of compact gray-brown soil with many tufo inclusions ranging in size from pebbles to fist-sized; tufo included fragments of gray, red, and yellow tufo. The layer is most likely the result of both natural accumulation and decay of the tufo bedrock. It is the bottom-most layer filling the cut SU418, which may be related to a tree planting (the pile of stones SU424 and reddish-orange fill above SU415).