A military structure located near Concord, California, within the grounds of the former Concord Naval Weapons Station. The site's designation 'S33-28' suggests it may be a specific grid reference or site identifier used in military mapping or inventory systems for the extensive munitions storage and support facilities historically present at this location. The Concord Naval Weapons Station was a major U.S.
Navy logistics and munitions depot throughout the Cold War and into the 21st century, supporting the Pacific Fleet. The current status and specific function of this particular structure are not confirmed by available sources.