| Name | What | Region | Country | Lat | Long | Elev ft. | Pop est |
|---|---|---|---|---|---|---|---|
| Olancha | city | California | United States | 36.28 | -118.01 | 3645 | |
| Olcott | city | California | United States | 38.28 | -121.82 | 16 | |
| Old Adobe | city | California | United States | 35.74 | -120.70 | 830 | |
| Old Bailey Place | city | California | United States | 39.17 | -123.48 | 830 | |
| Old Bretz Mill | city | California | United States | 37.08 | -119.30 | 5869 | |
| Old Chinatown (historical) | city | California | United States | 34.06 | -118.24 | 324 | |
| Old Corral | city | California | United States | 37.36 | -119.61 | 3428 | |
| Old Dale | city | California | United States | 34.12 | -115.80 | 1669 | |
| Old Forbestown | city | California | United States | 39.53 | -121.28 | 2811 | |
| Old Fort Jim | city | California | United States | 38.71 | -120.72 | 2509 | |
| Old Garlock | city | California | United States | 35.38 | -117.83 | 1994 | |
| Old Gilroy | city | California | United States | 37.00 | -121.53 | 164 | |
| Old Hilltown | city | California | United States | 36.63 | -121.67 | 42 | |
| Old Hopland | city | California | United States | 38.98 | -123.10 | 830 | |
| Old Hulbert Place | city | California | United States | 41.44 | -121.05 | 5029 | |
| Old Mammoth | city | California | United States | 37.63 | -118.98 | 8389 | |
| Old Mill Park Mobile Home Park | city | California | United States | 36.99 | -121.96 | 68 | |
| Old Ornbaun Hot Springs | city | California | United States | 38.91 | -123.31 | 1669 | |
| Old Pino | city | California | United States | 38.82 | -120.65 | 3398 | |
| Old Point Comfort | city | California | United States | 34.42 | -117.83 | 4320 | |
| Old Red Rock Place | city | California | United States | 38.79 | -123.44 | 1669 | |
| Old River | city | California | United States | 35.27 | -119.11 | 331 | |
| Old Station | city | California | United States | 40.68 | -121.43 | 4396 | |
| Old Town | city | California | United States | 35.14 | -118.49 | 4189 | |
| Old Town | city | California | United States | 34.40 | -119.53 | 88 | |
| Old Town | city | California | United States | 38.10 | -122.57 | 59 | |
| Old Town | city | California | United States | 34.22 | -119.05 | 111 | |
| Old Town San Diego | city | California | United States | 32.75 | -117.20 | 118 | |
| Oleander | city | California | United States | 36.63 | -119.75 | 236 | |
| Olema | city | California | United States | 38.04 | -122.79 | 78 | |
| Oleo (historical) | city | California | United States | 33.92 | -117.88 | 337 | |
| Oleum | city | California | United States | 38.04 | -122.25 | 85 | |
| Olga | city | California | United States | 34.11 | -118.17 | 830 | |
| Olig (historical) | city | California | United States | 35.32 | -119.66 | 1072 | |
| Olinda | city | California | United States | 40.44 | -122.41 | 830 | |
| Olinda (historical) | city | California | United States | 33.93 | -117.84 | 830 | |
| Olive | city | California | United States | 33.84 | -117.85 | 209 | |
| Olive Hill | city | California | United States | 39.29 | -121.47 | 249 | |
| Olive Springs (historical) | city | California | United States | 37.06 | -121.92 | 830 | |
| Olive View | city | California | United States | 34.32 | -118.44 | 1669 | |
| Olivehurst | city | California | United States | 39.10 | -121.55 | 59 | |
| Olivenhain | city | California | United States | 33.05 | -117.23 | 190 | |
| Oliver (historical) | city | California | United States | 39.13 | -121.59 | 55 | |
| Olympia | city | California | United States | 37.07 | -122.06 | 396 | |
| Olympia Glade | city | California | United States | 39.23 | -121.04 | 2621 | |
| Olympic Heights | city | California | United States | 39.34 | -120.16 | 5869 |