Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| Onyx | Populated Place | 852 | Kern | 35 41 25 N | 118 13 14 W |
| Onyx Mine | Mine | 871 | Inyo | 36 03 02 N | 117 22 54 W |
| Onyx Mine | Mine | 764 | San Bernardino | 34 47 53 N | 115 58 02 W |
| Onyx Mine | Mine | 2404 | San Bernardino | 34 11 18 N | 116 41 04 W |
| Onyx Peak | Summit | 1594 | Kern | 35 39 25 N | 118 13 35 W |
| Onyx Ranch | Locale | 830 | Kern | 35 41 43 N | 118 14 31 W |
| Onyx Spring | Spring | 2525 | San Bernardino | 34 11 22 N | 116 41 54 W |
| Onyx Summit | Gap | 2576 | San Bernardino | 34 11 32 N | 116 43 08 W |
| Oo-moo-chah (historical) | Populated Place | 14 | Sacramento | 38 24 30 N | 121 22 19 W |
| Opal Canyon | Valley | | Inyo | 37 05 31 N | 117 57 50 W |
| Opal Cliff Park Mobile Home Park (subdivision) | Populated Place | 16 | Santa Cruz | 36 57 54 N | 121 57 59 W |
| Opal Cliffs | Populated Place | 10 | Santa Cruz | 36 57 39 N | 121 57 51 W |
| Opal Cliffs Drive Overlook | Locale | 7 | Santa Cruz | 36 57 51 N | 121 57 40 W |
| Opal Creek | Stream | | Santa Cruz | 37 09 54 N | 122 13 30 W |
| Opal Hill | Summit | 111 | Calaveras | 38 05 36 N | 120 53 28 W |
| Opal Hill Mine | Mine | 224 | Riverside | 33 27 06 N | 114 51 56 W |
| Opal Mine | Mine | 2225 | Inyo | 37 04 06 N | 117 59 56 W |
| Opal Mountain | Summit | 1137 | San Bernardino | 35 09 39 N | 117 11 20 W |
| Opal Staniek Tot Lot | Park | 18 | Alameda | 37 53 06 N | 122 17 37 W |
| Opapee Creek | Stream | | Plumas | 39 59 07 N | 121 16 53 W |
| Opdyke Cow Camp | Locale | 1677 | Lassen | 40 42 27 N | 120 54 57 W |
| Opdyke Hill | Summit | 1418 | Shasta | 40 48 29 N | 121 31 42 W |
| Opegoi (historical) | Populated Place | 104 | Humboldt | 41 15 34 N | 123 36 22 W |
| Open Bible Church | Church | | Los Angeles | 34 04 13 N | 118 05 49 W |
| Open Bible Church | Church | 66 | Santa Clara | 37 15 04 N | 121 54 34 W |
| Open Door Christian Church | Church | 9 | Sonoma | 38 13 54 N | 122 38 24 W |
| Open Door Church | Church | 14 | San Luis Obispo | 35 06 01 N | 120 36 38 W |
| Open Door Church of God in Christ | Church | | Los Angeles | 33 52 26 N | 118 12 06 W |
| Open Door Church of God in Christ | Church | | Los Angeles | 34 08 22 N | 117 59 34 W |
| Open Door Community Church | Church | 43 | Sonoma | 38 26 44 N | 122 43 52 W |
| Open Door House of Prayer | Church | 7 | San Joaquin | 37 56 03 N | 121 15 24 W |
| Open Door Mission Church | Church | 101 | Tulare | 36 32 13 N | 119 23 28 W |
| Open Door Mission of Deliverance | Church | 5 | Contra Costa | 37 57 03 N | 122 22 04 W |
| Open Ridge | Ridge | 930 | Glenn | 39 27 56 N | 122 39 21 W |
| Opera Plaza (subdivision) | Populated Place | 26 | San Francisco | 37 46 53 N | 122 25 15 W |
| Operating Engineers Pension Trust Building Heliport | Airport | 78 | Los Angeles | 34 03 43 N | 118 17 31 W |
| Operation Fresh Start Apostolic Faith Church | Church | 127 | Kern | 35 24 24 N | 119 01 35 W |
| Ophir | Populated Place | 208 | Placer | 38 53 28 N | 121 07 25 W |
| Ophir Canal | Canal | 373 | Placer | 38 55 05 N | 121 07 02 W |
| Ophir Elementary School | School | 234 | Placer | 38 53 46 N | 121 07 32 W |
| Ophir Hill | Summit | 836 | Nevada | 39 12 16 N | 121 02 30 W |
| Ophir Hill Acres | Populated Place | 882 | Nevada | 39 11 35 N | 121 02 26 W |
| Ophir Mine | Mine | 669 | Inyo | 35 50 03 N | 117 17 03 W |
| Ophir Mine | Mine | 1187 | Sierra | 39 27 54 N | 120 50 14 W |
| Ophir Mine | Mine | 991 | Tuolumne | 37 59 50 N | 120 13 30 W |
| Ophir Mountain | Summit | 1833 | Inyo | 36 17 25 N | 117 35 56 W |
| Opium Glade Ridge | Ridge | 1599 | Tehama | 40 08 45 N | 122 56 55 W |
| Opportunity Baptist Church | Church | 67 | Los Angeles | 34 01 19 N | 118 15 20 W |
| Opportunity School | School | 7 | Monterey | 36 36 04 N | 121 52 00 W |
| Opportunity SubSection Number 4 Prospect | Mine | 1763 | Kern | 35 32 24 N | 118 27 38 W |
| Optimists Home for Boys | Building | 218 | Los Angeles | 34 07 42 N | 118 11 18 W |
| Ora | Populated Place | 196 | Fresno | 36 09 05 N | 120 19 36 W |
| Ora Grande Mine | Mine | 1655 | Kern | 35 28 37 N | 118 09 03 W |
| Ora Lake | Lake | 516 | Lake | 39 03 53 N | 122 58 54 W |
| Ora Spring | Spring | 1758 | El Dorado | 38 43 52 N | 120 19 55 W |
| Orange | Populated Place | 58 | Orange | 33 47 16 N | 117 51 11 W |
| Orange Avenue Baptist Church | Church | | Orange | 33 49 33 N | 117 56 52 W |
| Orange Avenue Junction | Populated Place | 124 | Los Angeles | 34 05 33 N | 117 56 35 W |
| Orange Blossom Bridge | Bridge | 37 | Stanislaus | 37 47 18 N | 120 45 46 W |
| Orange Blossom Mine | Mine | 427 | Mariposa | 37 34 26 N | 120 12 47 W |
| Orange Blossom Mine | Mine | 866 | San Bernardino | 34 41 11 N | 115 47 11 W |
| Orange Blossom Recreation Area | Park | 38 | Stanislaus | 37 47 22 N | 120 45 47 W |
| Orange Blossom School (historical) | School | 56 | Stanislaus | 37 47 28 N | 120 44 25 W |
| Orange Blossom Wash | Stream | | San Bernardino | 34 35 13 N | 115 39 00 W |
| Orange Center Elementary School | School | 85 | Fresno | 36 40 58 N | 119 46 52 W |
| Orange City Hall | Building | 59 | Orange | 33 47 14 N | 117 51 02 W |
| Orange Coast College | School | 20 | Orange | 33 40 10 N | 117 54 42 W |
| Orange County | Civil | 49 | Orange | 33 42 00 N | 117 46 03 W |
| Orange County Army Air Field (historical) | Military (Historical) | 14 | Orange | 33 40 30 N | 117 52 05 W |
| Orange County Chinese Christian Church | Church | | Orange | 33 46 02 N | 117 57 27 W |
| Orange County Community Hospital | Hospital | 19 | Orange | 33 49 52 N | 118 00 50 W |
| Orange County Courthouse | Building | 38 | Orange | 33 45 01 N | 117 52 09 W |
| Orange County Fairgrounds | Park | 20 | Orange | 33 39 57 N | 117 54 08 W |
| Orange County Marine Institute | Locale | 55 | Orange | 33 27 42 N | 117 42 30 W |
| Orange County Public Library - University Park Branch | Building | 26 | Orange | 33 39 39 N | 117 49 14 W |
| Orange County Reservoir 35-007 Dam | Dam | 49 | Orange | 33 56 12 N | 117 53 03 W |
| Orange County Steel Salvage Heliport | Airport | 67 | Orange | 33 50 53 N | 117 51 03 W |
| Orange County Young Nak Presbyterian Church | Church | | Orange | 33 46 48 N | 117 55 07 W |
| Orange Cove | Populated Place | 129 | Fresno | 36 37 28 N | 119 18 49 W |
| Orange Cove City Hall | Building | 129 | Fresno | 36 37 29 N | 119 18 47 W |
| Orange Cove Plaza Shopping Center | Locale | 126 | Fresno | 36 37 18 N | 119 19 35 W |
| Orange Cove Post Office | Post Office | 130 | Fresno | 36 37 29 N | 119 18 42 W |
| Orange Covenant Church | Church | | Orange | 33 47 07 N | 117 49 08 W |
| Orange Crest Number 2 Park | Park | 542 | Riverside | 33 53 34 N | 117 18 31 W |
| Orange Drain | Canal | -15 | Imperial | 32 57 09 N | 115 21 43 W |
| Orange Fair Shopping Center | Locale | 47 | Orange | 33 51 28 N | 117 55 23 W |
| Orange Flat | Flat | 572 | San Luis Obispo | 35 25 08 N | 120 40 05 W |
| Orange Glen Elementary School | School | 219 | San Diego | 33 08 43 N | 117 02 08 W |
| Orange Glen High School | School | 218 | San Diego | 33 07 44 N | 117 02 26 W |
| Orange Grove Adult School | School | 29 | Sacramento | 38 38 53 N | 121 21 19 W |
| Orange Grove Elementary School | School | 71 | Los Angeles | 33 59 49 N | 118 03 36 W |
| Orange Grove Middle School | School | 155 | Los Angeles | 34 00 40 N | 117 59 44 W |
| Orange Grove Park | Park | 222 | Los Angeles | 34 09 23 N | 118 03 08 W |
| Orange High School | School | 65 | Orange | 33 47 46 N | 117 50 51 W |
| Orange Hills Baptist Church | Church | | Orange | 33 46 30 N | 117 48 34 W |
| Orange Korean Church | Church | | Orange | 33 52 31 N | 117 56 15 W |
| Orange Lateral | Canal | -16 | Imperial | 32 57 12 N | 115 21 51 W |
| Orange Memorial Park | Cemetery | 8 | San Mateo | 37 39 15 N | 122 25 37 W |
| Orange Mobile Home Park (subdivision) | Populated Place | 81 | Orange | 33 49 30 N | 117 50 00 W |
| Orange Park Acres | Populated Place | 146 | Orange | 33 48 07 N | 117 46 56 W |
| Orange Post Office | Post Office | | Orange | 33 48 20 N | 117 50 05 W |
| Orange Public Library | Building | 60 | Orange | 33 47 17 N | 117 50 59 W |
| Orange Seventh Day Adventist Church | Church | | Orange | 33 47 41 N | 117 50 24 W |
| Orange Station (historical) | Locale | 46 | Orange | 33 46 43 N | 117 52 40 W |
| Orange Street Kindergarten | School | 68 | Santa Barbara | 34 56 57 N | 120 25 53 W |
| Orange Street Mini Park | Park | 140 | Tulare | 36 03 42 N | 119 01 13 W |
| Orange Street Plaza Shopping Center | Locale | 415 | San Bernardino | 34 03 40 N | 117 10 56 W |
| Orange Town and Country North Shopping Center | Locale | 46 | Orange | 33 46 38 N | 117 51 59 W |
| Orange Town and Country South Shopping Center | Locale | 48 | Orange | 33 46 32 N | 117 51 58 W |
| Orange Tree Plaza Shopping Center | Locale | 70 | Sacramento | 38 40 45 N | 121 13 29 W |