California - Role: Building
| Nystrom Elementary School-The Maritime Building |
| Oak Grove Butterfield Stage Station |
| Oakland Auditorium |
| Oakland City Hall |
| Oakland Free Library-23rd Avenue Branch |
| Oakland Free Library-Alden Branch |
| Oakland Free Library-Golden Gate Branch |
| Oakland Free Library-Melrose Branch |
| Oakland Hotel |
| Oakland Iron Works-United Works, and the Remillard Brick Company |
| Oakland Lamp Works |
| Oakland Public Library |
| Oakland YWCA Building |
| Oaks, The |
| Oakville Grocery |
| Oceanside City Hall and Fire Station |
| Octagon Building |
| Odd Fellows Building |
| Oddfellows Hall |
| Odd Fellows Hall |
| Odd Fellows Hall |
| Odd Fellows Hall |
| Odd Fellows Temple |
| O'Donnell, Thomas, House |
| Offerman, John, House |
| Ohlandt Newlyweds House |
| Ohm, John, House |
| Old Administration Building, Fresno City College |
| Old Adobe Barn |
| Old Backs House |
| Old Bank of America Building |
| Old City Hall |
| Old City Hall Building |
| Old Farmdale School |
| Old Jacoby Creek School |
| Old La Grange Schoolhouse |
| Old Masonic Hall |
| Old Napa Register Building |
| Old Ohio Street Houses |
| Old Petaluma Opera House |
| Old Post Office |
| Old San Antonio Hospital |
| Old Santa Rosa Catholic Church and Cemetery |
| Old Tavern |
| Old U.S. Mint |
| Old Weber School |
| Old YWCA Building |
| Olinsky Building |
| Olivas Adobe |
| Olive Civic Center |
| Olivenhain Town Meeting Hall |
| Olsen, Donald and Helen, House |
| Olvida Penas |
| One Lombard Street |
| Ontario and San Antonio Heights Waiting Station |
| Ontario Baseball Park |
| Ontario State Bank Block |
| Orange County Courthouse |
| Orange Cove Santa Fe Railway Depot |
| Orange Grove Court |
| Orange Intermediate School-Central Grammar School |
| Orange Lawn |
| Orange Union High School |
| Orosi Branch Library |
| Oroville Carnegie Library |
| Oroville Chinese Temple |
| Oroville Commercial District (old) |
| Oroville Inn |
| Ostrander Lake Ski Hut |
| Osuna, Juan Maria, Adobe |
| Otis Elevator Company Building |
| Ott's Assay Office |
| Our Lady of the Wayside |
| Outdoor Art Club |
| Outlands in the Eighty Acres |
| Oviatt, James, Building |
| Oxnard Public Library |
| Pacheco, Don Fernando, Adobe |
| Pacific Biological Laboratories |
| Pacific Coast Railway Company Grain Warehouse |
| Pacific Electric Building |
| Pacific Electric Etiwanda Depot |
| Pacific Electric Railway Company Depot |
| Pacific Electric Railway Company Substation No. 8 |
| Pacific Electric Sub-Station No. 14 |
| Pacific Gas and Electric Company General Office Building and Annex |
| Pacific Gas and Electric Company Substation J |
| Pacific Gas & Electric Company Building |
| Pacific Press Building |
| Packard Library |
| Paddison Ranch Buildings |
| Padua Hills Theatre |
| Paige Motor Car Co. Building |
| Palace Hotel |
| Palace of Fine and Decorative Arts, Treasure Island |
| Palmer, Annie, House |
| Palmer, Judge Augustus C., House |
| Palmer, Minnie Hill, House |
| Palmetto Court |
| Palm Springs Aerial Tramway Mountain Station |
Data from United States Park Service and Wikidata
