In the 1980s, to relieve overcrowding in existing on-campus library buildings, the UC system constructed two regional library facilities: the Northern Regional Library Facility at UC Berkeley's Richmond Field Station (opened 1982), and the Southern Regional Library Facility on the western edge of the UCLA campus (opened 1987). As of 2019, Northern Regional Library Facility is home to 7.4 million volumes, while Southern Regional Library Facility is home to 6.5 million. Each facility receives items from all UC campuses in its respective region of the state, and has climate controls and high-density stacks. Items are shelved two deep and are arranged in a sequence that results in efficient use of space (but is not quite as intuitive as traditional library indexing systems). As a result, casual browsing is prohibited, and the shelves are accessible only by library clerks trained to retrieve and put back items properly. Users must page materials to an on-site reading room or to a library at their home campus.