Mariposa, CA
Transparent derived index from EPA TRI / SDWIS / Superfund extracts: not an official EPA rating. Fixed caps: facilities ≤25 pts (50+ = max), log10 releases ≤25 pts, Superfund ≤25 pts (5/site), health-violation systems ≤15 pts (3/system), high-chemical facilities ≤10 pts. Bands: High ≥60, Moderate ≥30. See methodology.
Environmental data for Mariposa in California · Population: 17,060
TRI sites such as US Natl Park Service Yosemite Natl Park; SDWIS systems such as MARIPOSA PUBLIC UTILITY DIST; YOSEMITE NPS-YOSEMITE VALLEY; PONDEROSA BASIN MUTUAL WTR CO anchor Mariposa, CA's EPA extract. Derived burden score 21/100 (Low Risk) uses fixed national caps on density, log release volume, Superfund count, and health-flagged systems - not an official EPA rating.
Health-flagged SDWIS rows in Mariposa include MARIPOSA PUBLIC UTILITY DIST; MARIPOSA PINES MUTUAL; YOSEMITE TERRACE ESTATES, while US Natl Park Service Yosemite Natl Park leads reported TRI pounds among local Form R filers. AQS median AQI 45 / peak 133 in 2024.
Burden score 21/100 (Low Risk) is the only weighted composite on this page. The tables below list every TRI facility, SDWIS system, and Superfund site EPA has on record for Mariposa -- not just the names called out above -- reproducing the disclosure history as filed, not a current-safety verdict. Extract current as of 2026-08-25.
Air Quality History (2020–2024)
EPA Air Quality Index (AQI) data showing how many days per year fall into each air quality category.
| Year | Good | Moderate | Unhealthy (SG) | Max AQI |
|---|---|---|---|---|
| 2024 | 255 (70%) | 105 | 6 | 133 |
| 2023 | 217 (59%) | 131 | 10 | 264 |
| 2022 | 211 (58%) | 125 | 8 | 198 |
| 2021 | 193 (53%) | 140 | 25 | 162 |
| 2020 | 195 (53%) | 123 | 27 | 1073 |
Source: EPA Air Quality System (AQS) Annual AQI by County AQI categories: Good (0-50), Moderate (51-100), Unhealthy for Sensitive Groups (101-150), Unhealthy (151-200), Very Unhealthy (201-300), Hazardous (301+)
For real-time air quality readings and pollutant breakdowns in California, see the EPA's AirNow.gov.
Water Systems (10)
| System | System pop (SDWIS) | Violations |
|---|---|---|
| MARIPOSA PUBLIC UTILITY DIST | 2,000 | 38 |
| YOSEMITE NPS-YOSEMITE VALLEY | 1,000 | 0 |
| PONDEROSA BASIN MUTUAL WTR CO | 798 | 0 |
| YOSEMITE NPS-EL PORTAL | 635 | 0 |
| YOSEMITE WEST WATER SYSTEM | 420 | 0 |
| MARIPOSA PINES MUTUAL | 284 | 2 |
| MPWD-COULTERVILLE CSA 1 | 193 | 0 |
| YOSEMITE NPS-WAWONA | 150 | 0 |
| YOSEMITE TERRACE ESTATES | 130 | 5 |
| YOSEMITE NPS-HODGDON MEADOW | 51 | 3 |
TRI Facilities (1)
| # | Facility | Total Releases |
|---|---|---|
| 1 | US Natl Park Service Yosemite Natl Park | 380 lbs |
Cities in Mariposa (4)
Frequently Asked Questions
What is the environmental risk level in Mariposa, California? ▼
Are there Superfund sites in Mariposa? ▼
How many toxic release facilities are in Mariposa? ▼
What is the air quality in Mariposa? ▼
Is the drinking water safe in Mariposa? ▼
What environmental agencies cover Mariposa? ▼
What does this county environmental profile show?
This county environmental profile rolls up EPA Toxics Release Inventory facility reports, Safe Drinking Water Information System public-water-system filings, and Superfund National Priorities List sites for the county boundary defined by the U.S. Census Bureau. Facility counts reflect facilities with a reporting address inside the county, not where downstream environmental effects may be observed. Population figures are from the most recent Census ACS 5-year estimate. The county detail page is updated whenever the upstream EPA programs publish revised data; see the methodology page for the documented ingest cadence and the editorial choices governing how aggregations are computed.
Read our methodology - how this data is sourced, computed, and verified.