Part of the Cwm y Llan slate quarry complex (401443), located at its E end, close to Bwlch Cwm Llan. Slate quarry up to 15m deep with steep and undercut sides, irregular shape c5 x 10m; loose slate in base; good drill marks to walls. Cut into hillside to N with access passage leading in from S.
Inside the quarry pit, an adit of unknown extent runs into the ground towards WNW, The entrance is c2m high and 2m wide with a square cut top. The level itself is 1.5m high and 1m wide; it curves round towards NW, then out of sight.
Recorded as part of RCAHMW Uplands Initiative Project. W.B. Horton, H&H, 7/9/2011.