Skip to content
RADON411

Locations and reports

Radon Levels in Tuolumne County, California

EPA puts Tuolumne County in Zone 2, its middle radon zone, and 23.0% of its 74 reported radon tests (2008 to 2017, laboratory totals) were at or above 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    23.0%

    12.7 pts above CA

    Tuolumne
    23.0%
    California
    10.3%

    74 tests, 2008 to 2017

  • Median result

    1.4pCi/L

    Below action level

    Tuolumne
    1.4 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    74

    25th of 33 by tests

    Tuolumne
    74
    Los Angeles
    2,363

    Reported to CDC before any fix, 2008 to 2017

  • EPA radon zone

    Zone 2

    Moderate potential

    1. 1
    2. Zone 2
    3. 3

    1 highest, 3 lowest

    EPA predicts 2 to 4 pCi/L indoors

  • Rank in California

    5 of 33

    Top quarter

    Tuolumne
    23.0%
    El Dorado
    30.3%

    By share, of 33 with 30+ tests

Read a result for Tuolumne County

Starts at Tuolumne County's median, 1.4 pCi/L

1.4pCi/L

EPA’s own thresholds; the figures are the area’s, never this home’s.

EPA’s reading of 1.4 pCi/L

Below 2 pCi/L

  1. Under 20 to 1.9 pCi/L
  2. 2 to 4consider a fix
  3. 4 and aboveEPA says fix it

This result is below 2 pCi/L, the level at which EPA says a fix should be considered. Tuolumne County's median reported result, 2008 to 2017.

Interpret this reading

The data

Tuolumne County, At a glance

Tuolumne County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Tuolumne County is a county: EPA's forecast for it as a whole is an average indoor of 2 to 4 pCi/L (75 to 150 Bq/m³). It describes no single address, and homes above EPA's are found in every zone, this one included.

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 Tuolumne County, 2008 to 2017, laboratory

Reported results by concentration band, Tuolumne County, 2008 to 2017, laboratory
Under 2 pCi/L: 57%2 to 4 pCi/L: 20%4 pCi/L and above: 23%

Of 74 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Tuolumne County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L4256.8%
2 to 4 pCi/L1520.3%
4 pCi/L and above1723.0%
What these figures count

These are the 74 tests reported to CDC for Tuolumne County over 2008 to 2017 (laboratory totals), many from homes being sold or already suspected of a problem: they describe the county's reported tests, not this house.

Measured: CDC tracking data. Figure above: 2008 to 2017, laboratory. Measured data period: 2005 to 2017 (every CDC figure on file).

How to read these figures

Tuolumne County, Compared

Tuolumne County radon figures, compared

Calculated by Radon411

Tuolumne County's 74 reported tests over the 2008 to 2017 laboratory totals had a middle value of 1.4 pCi/L and a maximum of 58.9 pCi/L, and 23.0% reached 4 pCi/L. California as a whole (56 California counties, pooled) comes to 10.3%: 12.7 points lower than here.

Among its state's counties it ranks 5th of 33 California counties with 30 or more tests for the same period. Statewide for the same period, El Dorado County reported the highest share (30.3%) and Sonoma County the lowest (0.8%).

Below the action level, 42 tests (56.8%) came in under 2 pCi/L, against 76.8% statewide, and 15 tests (20.3%) fell between 2 and 4, against 12.9% statewide. CDC's ten-year totals for Tuolumne County went from 65 tests (2005 to 2014) to 74 (2008 to 2017), the share going from 24.6% to 23.0%.

EPA's 1993 zone map puts Tuolumne County in Zone 2, a predicted county average between 2 and 4 pCi/L. USGS geology rates 100% of the county's land moderate radon potential.

Next door, the shares run from 14.7% in Madera County to 17.6% in Calaveras County, with Calaveras County and Madera County below Tuolumne County.

Tuolumne County against California, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Tuolumne County
Tuolumne County7423.0%1.4 pCi/LThis county
California, pooled56 counties, pooled9,41510.3%Not pooled−12.7 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+12.7 points
El Dorado Countyhighest in the state27430.3%1.6 pCi/L+7.3 points
Sonoma Countylowest in the state1310.8%0.5 pCi/L−22.2 points
Alpine County, CAborders it1963.2%4.5 pCi/L+40.2 points
Mono County, CAborders it2050.0%4.6 pCi/L+27.0 points
Calaveras County, CAborders it3417.6%1.7 pCi/L−5.4 points
Mariposa County, CAborders it616.7%1.3 pCi/L−6.3 points
Madera County, CAborders it3414.7%1.4 pCi/L−8.3 points
Stanislaus County, CAborders it2711.1%1.4 pCi/L−11.9 points
Merced County, CAborders it50.0%2.1 pCi/L−23.0 points
Where Tuolumne County's reported results fell, 2008 to 2017, laboratory, beside California and the United States
ResultTuolumne County testsTuolumne County shareCalifornia shareU.S. shareAgainst California
Under 2 pCi/L4256.8%76.8%39.6%−20.0 points
2 to 4 pCi/L1520.3%12.9%24.7%+7.4 points
4 pCi/L and above1723.0%10.3%35.7%+12.7 points
Tuolumne County ranked among the 33 California counties with 30 or more tests, by share at or above 4 pCi/L, 2008 to 2017, laboratory
CountyRankTestsAt or above 4 pCi/LMedian
El Dorado County1 of 3327430.3%1.6 pCi/L
Amador County2 of 333627.8%2.3 pCi/L
Nevada County3 of 3326025.0%2.0 pCi/L
Tulare County4 of 338023.8%1.7 pCi/L
Tuolumne County5 of 337423.0%1.4 pCi/L
Santa Cruz County6 of 3310521.9%1.2 pCi/L
Calaveras County7 of 333417.6%1.7 pCi/L
Santa Barbara County8 of 3342117.6%1.2 pCi/L
Solano County9 of 333815.8%0.9 pCi/L
Monterey County10 of 338714.9%0.8 pCi/L
San Joaquin County11 of 337414.9%1.4 pCi/L
Tuolumne County ten-year laboratory totals, against California's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestCalifornia, pooledChange from the row before
2008 to 20177423.0%1.4 pCi/L58.9 pCi/L10.3%−3.2 points
2007 to 20166526.2%1.9 pCi/L58.9 pCi/L10.6%−1.9 points
2006 to 20156428.1%1.9 pCi/L58.9 pCi/L10.6%+3.5 points
2005 to 20146524.6%1.5 pCi/L58.9 pCi/L10.0%First on file

Pooled shares: Radon411's sum of CDC's county counts for one period.

Tuolumne County, Geology

The ground under Tuolumne County

Predicted

USGS's geologic map puts all of Tuolumne 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).

USGS's geologic areas under Tuolumne County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Sierra NevadaNorthern Sierra Nevada is underlain primarily by Paleozoic and Mesozoic metamorphic rocks. Granitic rocks predominate in the southern Sierrra Nevada , with lesser Mesozoic metamorphic rocks.Moderate9100%

Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.

Tuolumne County beside the ground around it

Across California 0.1% of the land is rated high; none of Tuolumne County's is. Of the 7 counties that border it, none has as large a share of moderate-potential ground; Alpine County comes nearest at 100%.

Share of land by USGS radon potential: Tuolumne County, the 7 counties bordering it and California
AreaEPA zoneLow potentialModerate potentialHigh potential
Tuolumne CountyZone 2None100%None
Mariposa CountyZone 2None100%None
Alpine CountyZone 2None100%None
Calaveras CountyZone 2None100%None
Mono CountyZone 2None100%None
Madera CountyZone 236.6%63.4%None
Stanislaus CountyZone 349.1%50.9%None
Merced CountyZone 365.2%34.8%None
California58 counties, pooled by land areaVaries57.2%42.6%0.1%

The map rates the ground, not the air in any home.

Local help

Tuolumne County, Local resources

Radon testing and mitigation in Tuolumne County

What California's program says
Phone
1-800-745-7236
Email
Radonprogram@cdph.ca.gov
Licensing of radon professionals
The Radon Program certifies all radon service providers operating in California.

What it means

Tuolumne County, Questions

Questions about radon in Tuolumne County

Are radon levels high in Tuolumne County?

Over the 2008 to 2017 laboratory totals, 23.0% of the radon tests reported to CDC for Tuolumne County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.4 pCi/L. Of 33 California counties with 30 or more tests for the same period, 4 reported a higher share; pooled, the state comes to 10.3%.

Which counties border Tuolumne County?

Tuolumne County borders 7 counties: Mariposa County, Alpine County, Calaveras County, Mono County, Madera County, Stanislaus County and Merced County.

Products

Tuolumne County, Products

Testing a home in Tuolumne County

In Tuolumne County, 23.0% of 74 tests reported to CDC over the 2008 to 2017 laboratory totals reached 4 pCi/L, against 10.3% pooled across California. In Zone 2 a short-term kit (2 to 90 days) is the quick first check in Tuolumne County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Tuolumne County homes, compared

Explore

Tuolumne County, Bordering counties

Counties bordering Tuolumne County

Calculated by Radon411

Tuolumne County, Cities and towns

Cities and towns in Tuolumne County

About 53,160 people live in Tuolumne County by the Census Bureau's estimate for July 1, 2025, 2,209 fewer than in 2020 (−4.0%). That works out to 24 people per square mile of land. Sonora, its one incorporated place, has 4,866 residents, 9.2% of the total. Testing is reported here more often than across the state: CDC's 74 reported tests for 2008 to 2017 come to 1.4 for every 1,000 residents (2025 estimate), against 0.2 for California.

Sonora is the one incorporated place here; CDC publishes no figure by town, so it reads Tuolumne County's.

Sonora, Tuolumne County: residents on July 1, 2025
PlaceResidentsSince 2020Share of residents
Sonora4,866−2.5%9.2%

One incorporated place, as listed in the U.S. Census Bureau’s 2020 place reference files. Residents: U.S. Census Bureau population estimates for July 1, 2025 (Vintage 2025).

Tuolumne County, Homes

Homes in Tuolumne County

Tuolumne County is a place of houses on their own lots: 81% of its 31,491 homes are detached single-family houses, against 57% across California. Half of its homes were built before 1979, close to California's 1976: 16% date from before 1960 and 12% from 2000 or later. 74% 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 in Tuolumne County, California, 2019 to 2023
HomesTuolumne CountyCalifornia
Housing units31,49114,532,683
Detached houses81%57%
In buildings of 5 or more5%24%
Mobile homes8%4%
Built before 196016%27%
Built since 200012%18%
Middle year built19791976
Owner-occupied74%56%

Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.