Roughly EW wall serving as Northern boundary for area that appears to be a room, with mostly ashlar masonry composed of tufa and basalt blocks and covered by intermittent patches of rubble (under 4018). Also forms corner with portion of blocks from SU 4023, creating a NW corner for enclosed area. Seems to pass into E excavation limit and continue to E. S face exposed fully on W by excavation of collapse layer 4022 (partly collapse of wall 4007); SE face covered by remains of layer 4022 and N face completely covered by layer 4018. Shot in and photographed in 2011, to be photomodeled in 2012 when fully exposed.