| Month | Temp. (min) | Temp. (max) | Temp. (avg) | Precipitation |
| January | 38°F | 58°F | 47°F | 2.4" |
| February | 42°F | 64°F | 52°F | 1.9" |
| March | 46°F | 70°F | 57°F | 1.7" |
| April | 49°F | 76°F | 61°F | 1.3" |
| May | 54°F | 85°F | 69°F | 0.4" |
| June | 60°F | 93°F | 76°F | 0.2" |
| July | 64°F | 98°F | 80°F | 0.0" |
| August | 63°F | 96°F | 78°F | 0.0" |
| September | 59°F | 91°F | 74°F | 0.1" |
| October | 52°F | 80°F | 64°F | 0.7" |
| November | 44°F | 68°F | 54°F | 1.1" |
| December | 38°F | 58°F | 47°F | 2.3" |
| Index | Vallecito | California | National |
| Air quality index | 39 | 55 | 42 |
| Pollution index | 1,947,800 | 10,473,190 | 2,726,193 |
| Measurement | Total |
| Days measured | 365 |
| Days with good air quality | 331 |
| Days with moderate air quality | 33 |
| Days w/ poor A.Q. for sensitive groups | 1 |
| Days with unhealthy air quality |
| Pollutant | Total |
| Arsenic | 0.003% |
| Benzene | 0.030% |
| Carbon Tetrachloride | 0.000% |
| Lead | 0.010% |
| Mercury | 0.000% |
| City | Population | Air Quality Index | National Avg. |
| Angels, CA | 3,889 | 39 | 22.0% |
| Chinese Camp, CA | 146 | 39 | 22.0% |
| East Sonora, CA | 2,672 | 39 | 22.0% |
| Mountain Ranch, CA | 318 | 39 | 22.0% |
| Sonora, CA | 4,832 | 39 | 22.0% |
| Vallecito, CA | 132 | 39 | 22.0% |
| City | Population | Air Quality Index | National Avg. |
| Yellow Bluff, AL | 132 | 52 | 4.0% |
| Otter Creek, FL | 132 | 35 | 30.0% |
| Blockton, IA | 132 | 43 | 14.0% |
| Geneva, IA | 132 | 15 | 70.0% |
| Havelock, IA | 132 | 37 | 26.0% |
| Vallecito, CA | 132 | 39 | 22.0% |
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