| Official Name: | Post Mountain, California |
| Settlement Type: | Census-designated place |
| Subdivision Type: | Country |
| Subdivision Type1: | State |
| Subdivision Type2: | County |
| Subdivision Name2: | Trinity |
| Population Total: | 3032 |
| Population As Of: | 2020 |
| Population Density Km2: | auto |
| Area Footnotes: | [1] |
| Area Total Km2: | 32.15 |
| Area Land Km2: | 32.15 |
| Area Water Km2: | 0.0 |
| Timezone: | Pacific (PST) |
| Utc Offset: | -8 |
| Timezone Dst: | PDT |
| Utc Offset Dst: | -7 |
| Elevation M: | 995 |
| Pushpin Map: | California#USA |
| Pushpin Label: | Post Mountain |
| Coordinates: | 40.4228°N -123.2222°W |
| Postal Code Type: | ZIP Code |
| Postal Code: | 96041 (Hayfork) |
| Area Code: | 530 |
| Blank Name: | FIPS code |
| Blank Info: | 06-58456 |
| Blank1 Name: | GNIS feature ID |
| Blank1 Info: | 2804441 |
Post Mountain is an unincorporated community and census-designated place (CDP) in Trinity County, California, United States. It is on the north side of California State Route 36, west of Red Bluff and east of U.S. Route 101 near Fortuna. Hayfork, the nearest post office, is to the north on California State Route 3. Its population is 3,032 as of the 2020 census. Post Mountain was not listed as a CDP prior to the 2020 census.