After further study, this is interpreted as probably the remains of a rubble foundation layer for a wall of the eastern side of the Area A structure. The fill of a robbing trench for that same wall is also possible, although unlikely based on the composition.
SU430 contains rubble, possibly the result of robbing from wall SU420. In the area immediately south of wall SU420 there is the highest density of rubble, with other rubble thinning to the south. Fill of robbing cut (SU437) of wall SU420.