Room 123B is the southern portion of subdivided 123W. It measures 3 x 2.3 m and is divided from 123A by a cobble-and-mortar wall built during the San Juan occupation. Only three strata were recorded in the room: two post-occupational layers and a structured trash deposit. Work ceased in the room early, and lower levels were never reached. Three features were found in Room 123B: two burials and the east-west wall that divided it from 123A. Clearly, the San Juan occupants used Room 123B to deposit trash and bury deceased individuals. Based on the architectural style, stratigraphy, and ceramic assemblage, Room 123B was created sometime after 1130 and before 1200.