Short-term kit
Radon Short Term Test Kit short-term charcoal radon test kit, lab fee included
- Lab fee included
Method: Charcoal
In home: 2 to 7 days
Locations and reports
Radon Levels in Mariposa County, California
EPA puts Mariposa County in Zone 2, its middle radon zone, and only 6 radon tests from it are on file with CDC (2008 to 2017, laboratory totals). Homes with elevated levels occur in all three zones, so only a test measures yours.
Data checked By Radon411Methodology
Highest bordering
23.0%
Tuolumne County
- Tuolumne
- 23.0%
- Madera
- 14.7%
2 of 4 neighbours have 30+ tests, 2008 to 2017
Nearest county
14.7%
Madera County, 26 miles
- Madera
- 14.7%
- California
- 10.3%
Share at 4+ pCi/L, 34 tests, 2008 to 2017
Ground above low
100.0%
57.3 pts above California
- Mariposa
- 100.0%
- California
- 42.7%
Share of land USGS rates moderate or high potential
Tests reported
12
Too few for a share
- Mariposa
- 12
- Needed
- 30
2005 to 2014, laboratory
EPA radon zone
Zone 2
Moderate potential
- 1
- Zone 2
- 3
1 highest, 3 lowest
EPA predicts 2 to 4 pCi/L indoors
Read a result for Mariposa County
Starts at EPA's action level
EPA’s own thresholds; the figures are the area’s, never this home’s.
EPA’s reading of 4.0 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
The data
Mariposa County, At a glance
Mariposa County at a glance
Predicted: EPA radon zone
EPA Zone 2: moderate predicted potential
Mariposa County is a
USGS geologic potential: Moderate across 100% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Mariposa County, 2008 to 2017, laboratory
CDC holds 6 reported tests for Mariposa County over the 2008 to 2017 laboratory totals, with a median of 1.3 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Mariposa County beside the counties around it is how this page reads it.
What these figures count
Only 6 tests were reported to CDC for Mariposa County over 2008 to 2017 (laboratory totals), and tests are often run on homes being sold or already suspected of a problem: so few describe neither the county nor this house.
Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).
Mariposa County, Compared
Mariposa County radon figures, compared
Calculated by Radon411CDC's largest figure for Mariposa County rests on 12 tests over the 2005 to 2014 laboratory totals, 1 of them at or above 4 pCi/L, so each test moves its share by 8.3 points and no rank or comparison is drawn from it. Results reached as high as 4.4 pCi/L, with a middle value of 2.0 pCi/L.
Of the counties bordering it, 2 have a figure over the 2008 to 2017 laboratory totals: Tuolumne County reported the largest share at or above 4 pCi/L, 23.0%, and Madera County the smallest, 14.7%. Farther out, Calaveras County (56 miles away) at 17.6%, Fresno County (59 miles away) at 11.0% and Amador County (72 miles away) at 27.8% have figures too. Pooled across 56 California counties, 10.3% of reported tests reached that level; across every county in the country with a figure, 35.7%.
Statewide for the same period, El Dorado County reported the highest share (30.3%) and Sonoma County the lowest (0.8%). EPA's 1993 map puts Mariposa County in Zone 2, its middle label: a predicted county average between 2 and 4 pCi/L. USGS geology rates 100% of the county's land moderate radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Mariposa County, Geology
The ground under Mariposa County
PredictedUSGS's geologic map puts all of Mariposa County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Sierra Nevada, to which USGS gives a radon index of 9, in the moderate band (9 to 11).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Sierra Nevada | Northern Sierra Nevada is underlain primarily by Paleozoic and Mesozoic metamorphic rocks. Granitic rocks predominate in the southern Sierrra Nevada , with lesser Mesozoic metamorphic rocks. | Moderate | 9 | 100% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Mariposa County beside the ground around it
Across California 0.1% of the land is rated high; none of Mariposa County's is. Of the 4 counties that border it, none has as large a share of moderate-potential ground; Tuolumne County comes nearest at 100%.
The map rates the ground, not the air in any home.
Local help
Mariposa County, Local resources
Radon testing and mitigation in Mariposa County
- California Indoor Radon ProgramCalifornia Indoor Radon Program, run by California Department of Public Health, licenses or certifies radon professionals and offers free or discounted test kits, and answers questions about testing and mitigation in California.Visit the program’s page(opens in a new tab)
- Free and low-cost kitsThe program says:
Discounted test kits can be purchased through our partner laboratory, Alpha Energy, for $14.95.
- Compare kits
- Professionals in California4 professionals are listed in California.
What California's program says
- Phone
- 1-800-745-7236
- Radonprogram@cdph.ca.gov
- Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.
What it means
Mariposa County, Questions
Questions about radon in Mariposa County
Are radon levels high in Mariposa County?
Over the 2008 to 2017 laboratory totals, 16.7% of the radon tests reported to CDC for Mariposa County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.3 pCi/L. Of the counties bordering it, 2 have a figure over the 2008 to 2017 laboratory totals: Tuolumne County reported the largest share at or above 4 pCi/L, 23.0%, and Madera County the smallest, 14.7%.
Which counties border Mariposa County?
Mariposa County borders 4 counties: Madera County, Tuolumne County, Merced County and Stanislaus County.
Products
Mariposa County, Products
Testing a home in Mariposa County
No CDC figure names Mariposa County; the nearest county with one, Madera County (26 miles away), reported 14.7% of its tests at or above 4 pCi/L over the 2008 to 2017 laboratory totals, the only reading nearby until a test of this home. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Mariposa County; a long-term test tells the year-round average.
Test kits and monitors3
See every kit and monitor
Long-term kit
RL116 long-term radon test kit
- Lab fee extra
Method: Alpha track
In home: 90 days to 12 months
Monitor
EcoBlu plug-in digital radon monitor with a display
- C-NRPP 2024/25: Not included
- Plug-in
- Alarm
- Screen
Method: Ion chamber
First reading: Within 10 minutes
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Mariposa County, Bordering counties
Counties bordering Mariposa County
Calculated by Radon411- Radon levels in Tuolumne CountyEPA zone 2
23.0%at or above 4 pCi/L
Median 1.4 pCi/L · 74 tests
- Radon levels in Madera CountyEPA zone 2
14.7%at or above 4 pCi/L
Median 1.4 pCi/L · 34 tests
- Radon levels in Stanislaus CountyEPA zone 3
11.1%at or above 4 pCi/L
Median 1.4 pCi/L · 27 tests
- Radon levels in Merced CountyEPA zone 3
0.0%at or above 4 pCi/L
Median 2.1 pCi/L · 5 tests
Mariposa County, Residents
Who lives in Mariposa County
About 16,918 people live in Mariposa County by the Census Bureau's estimate for July 1, 2025, 212 fewer than in 2020 (−1.2%). That works out to 12 people per square mile of land. Testing is reported here more often than across the state: CDC's 12 reported tests for 2005 to 2014 come to 0.7 for every 1,000 residents (2025 estimate), against 0.3 for California.
Census lists no incorporated place in Mariposa County: every home in it reads the county's figures.
Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).
Mariposa County, Homes
Homes in Mariposa County
Mariposa County is a place of houses on their own lots: 76% of its 9,796 homes are detached single-family houses, against 57% across California. Much of Mariposa County is recent building: 23% of its homes have gone up since 2000 and the middle year built is 1986, against 1976 for California. 75% of occupied homes are lived in by their owner (California: 56%); in the rest a tenant can run a test, but a fix is the landlord's to make.
| Homes | Mariposa County | California |
|---|---|---|
| Housing units | 9,796 | 14,532,683 |
| Detached houses | 76% | 57% |
| In buildings of 5 or more | 4% | 24% |
| Mobile homes | 16% | 4% |
| Built before 1960 | 14% | 27% |
| Built since 2000 | 23% | 18% |
| Middle year built | 1986 | 1976 |
| Owner-occupied | 75% | 56% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.