California frost dates: R
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Rackerby | Apr 1 | Nov 17 | 230 d | 9b |
| Rail Road Flat | May 7 | Oct 28 | 174 d | 9a |
| Raisin City | Jan 30 | Dec 11 | 315 d | 9a |
| Ramona | Mar 4 | Dec 4 | 275 d | 9b |
| Ranchita | Jan 10 | Jan 1 | 356 d | 9a |
| Rancho Cordova | Jan 12 | Dec 16 | 338 d | 9b |
| Rancho Cucamonga | Jan 4 | Dec 30 | 360 d | 10a |
| Rancho Mirage | Jan 9 | Jan 9 | 365 d | 10a |
| Rancho Palos Verdes | Jan 9 | Jan 5 | 361 d | 10b |
| Rancho Santa Fe | Jan 5 | Jan 2 | 362 d | 10a |
| Rancho Santa Margarita | rare frost | 10b | ||
| Randsburg | Mar 19 | Nov 25 | 251 d | 9a |
| Ravendale | May 16 | Oct 8 | 145 d | 6b |
| Raymond | Apr 24 | Nov 4 | 194 d | 9b |
| Red Bluff | Feb 22 | Nov 29 | 280 d | 9b |
| Red Mountain | Mar 19 | Nov 25 | 251 d | 9a |
| Redcrest | Mar 4 | Nov 22 | 263 d | 9b |
| Redding | Feb 8 | Dec 28 | 323 d | 9b |
| Redlands | Jan 27 | Dec 19 | 326 d | 10a |
| Redondo Beach | rare frost | 10b | ||
| Redway | Mar 10 | Dec 1 | 266 d | 9b |
| Redwood City | Jan 17 | Dec 12 | 329 d | 10a |
| Redwood Estates | Feb 2 | Dec 6 | 307 d | 10a |
| Redwood Valley | Apr 8 | Nov 6 | 212 d | 9a |
| Reedley | Jan 30 | Dec 11 | 315 d | 9b |
| Represa | Feb 25 | Dec 5 | 283 d | 9b |
| Rescue | Mar 31 | Nov 21 | 235 d | 9b |
| Reseda | Jan 24 | Dec 15 | 325 d | 10a |
| Rialto | Jan 10 | Jan 2 | 357 d | 10a |
| Richgrove | Jan 31 | Dec 8 | 311 d | 9b |
| Richmond | Jan 4 | Jan 2 | 363 d | 10a |
| Richvale | Jan 29 | Dec 7 | 312 d | 9b |
| Ridgecrest | Mar 11 | Nov 12 | 246 d | 8b |
| Rimforest | May 5 | Nov 2 | 181 d | 8a |
| Rio Dell | Feb 1 | Dec 19 | 321 d | 9b |
| Rio Linda | Feb 22 | Nov 24 | 275 d | 9b |
| Rio Nido | Mar 20 | Nov 13 | 238 d | 9b |
| Rio Oso | Feb 11 | Nov 30 | 292 d | 9b |
| Rio Vista | Jan 12 | Dec 19 | 341 d | 9b |
| Ripon | Feb 6 | Dec 1 | 298 d | 9b |
| River Pines | Mar 31 | Nov 21 | 235 d | 9a |
| Riverbank | Jan 31 | Dec 5 | 308 d | 9b |
| Riverdale | Feb 24 | Nov 22 | 271 d | 9a |
| Riverside | Jan 9 | Dec 25 | 350 d | 10a |
| Robbins | Feb 22 | Nov 24 | 275 d | 9b |
| Rocklin | Feb 25 | Dec 5 | 283 d | 9b |
| Rodeo | Jan 17 | Dec 27 | 344 d | 9b |
| Rohnert Park | Feb 28 | Nov 25 | 270 d | 9a |
| Rosamond | Apr 3 | Nov 1 | 212 d | 8b |
| Rosemead | Jan 4 | Jan 2 | 363 d | 10b |
| Roseville | Feb 25 | Dec 5 | 283 d | 9b |
| Ross | Jan 16 | Dec 18 | 336 d | 9b |
| Rough And Ready | Apr 10 | Nov 13 | 217 d | 9a |
| Round Mountain | Jun 3 | Sep 14 | 103 d | 9a |
| Rowland Heights | rare frost | 10a | ||
| Rumsey | Apr 10 | Nov 6 | 210 d | 9b |
| Running Springs | May 5 | Nov 2 | 181 d | 8a |
| Rutherford | Feb 3 | Dec 4 | 304 d | 9b |
| Ryde | Feb 9 | Dec 5 | 299 d | 9b |