The break-in, which was at 400 Hartz Ave., was discovered at about 8 a.m. Monday when workers arrived at the site, spokesman Geoff Gillette said.
They discovered that copper wiring, construction tools and other items were taken, Gillette said. Some damage was also reported.
Police are investigating the theft and looking for anyone who may have been near the site over the weekend and saw or heard anything unusual.
Anyone with information about the case is asked to call Detective Sgt. Allan Shields at (925) 314-3703.