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Radon Levels in San Bernardino County, California

EPA puts San Bernardino County in Zone 2, its middle radon zone, and most reported tests there come back low, though 4.5% of 178 (2008 to 2017, laboratory totals) reached 4 pCi/L. Homes with elevated levels occur in all three zones, so only a test measures yours.

Data checked By Radon411Methodology

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  • Share at 4+ pCi/L

    4.5%

    5.8 pts below CA

    San Bernardino
    4.5%
    California
    10.3%

    178 tests, 2008 to 2017

  • Median result

    0.7pCi/L

    Below action level

    San Bernardino
    0.7 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    178

    16th of 33 by tests

    San Bernardino
    178
    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

    27 of 33

    Lowest quarter

    San Bernardino
    4.5%
    El Dorado
    30.3%

    By share, of 33 with 30+ tests

Read a result for San Bernardino County

Starts at San Bernardino County's median, 0.7 pCi/L

0.7pCi/L

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

EPA’s reading of 0.7 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. San Bernardino County's median reported result, 2008 to 2017.

Interpret this reading

The data

San Bernardino County, At a glance

San Bernardino County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

San Bernardino 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: Low across 84% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for San Bernardino County, 2008 to 2017, laboratory

Reported results by concentration band, San Bernardino County, 2008 to 2017, laboratory
Under 2 pCi/L: 87%2 to 4 pCi/L: 8%4 pCi/L and above: 5%

Of 178 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, San Bernardino County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L15587.1%
2 to 4 pCi/L158.4%
4 pCi/L and above84.5%
What these figures count

These are the 178 tests reported to CDC for San Bernardino 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

San Bernardino County, Compared

San Bernardino County radon figures, compared

Calculated by Radon411

Only 8 of 178 radon tests reported for San Bernardino County over the 2008 to 2017 laboratory totals reached 4 pCi/L (4.5%). The median result, 0.7 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 10.1 pCi/L.

Across 56 California counties pooled together, 10.3% of tests reached that level, so San Bernardino County runs 5.8 points below its state. Against the national pool of 35.7%, the gap is 31.2 points lower. Its place in the state: 27th of 33 California counties with 30 or more tests for the same period.

The reported tests do not follow EPA's Zone 2 label for San Bernardino County (predicted average between 2 and 4 pCi/L): 4.5% of them reached 4 pCi/L, fewer than that label suggests. Of 6 neighbours with a figure, 3 reported a larger share at or above 4 pCi/L and 3 a smaller one; the spread is 1.3% (Riverside County) to 11.6% (Kern County).

Below the action level, 155 tests (87.1%) came in under 2 pCi/L, against 76.8% statewide, and 15 tests (8.4%) fell between 2 and 4, against 12.9% statewide. USGS geology rates 84% of the county's land low radon potential.

CDC's ten-year totals for San Bernardino County went from 162 tests (2005 to 2014) to 178 (2008 to 2017), the share going from 3.7% to 4.5%.

San Bernardino County against California, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from San Bernardino County
San Bernardino County1784.5%0.7 pCi/LThis county
California, pooled56 counties, pooled9,41510.3%Not pooled+5.8 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+31.2 points
El Dorado Countyhighest in the state27430.3%1.6 pCi/L+25.8 points
Sonoma Countylowest in the state1310.8%0.5 pCi/L−3.7 points
Inyo County, CAborders it1450.0%4.0 pCi/L+45.5 points
Kern County, CAborders it12111.6%1.8 pCi/L+7.1 points
Los Angeles County, CAborders it2,3639.5%0.7 pCi/L+5.0 points
Clark County, NVborders it2,5988.1%0.9 pCi/L+3.6 points
Mohave County, AZborders it494.1%0.2 pCi/L−0.4 points
Orange County, CAborders it4313.9%0.7 pCi/L−0.6 points
Riverside County, CAborders it2261.3%0.6 pCi/L−3.2 points
Where San Bernardino County's reported results fell, 2008 to 2017, laboratory, beside California and the United States
ResultSan Bernardino County testsSan Bernardino County shareCalifornia shareU.S. shareAgainst California
Under 2 pCi/L15587.1%76.8%39.6%+10.3 points
2 to 4 pCi/L158.4%12.9%24.7%−4.5 points
4 pCi/L and above84.5%10.3%35.7%−5.8 points
San Bernardino 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
Contra Costa County22 of 332858.8%0.9 pCi/L
Sacramento County23 of 331947.7%0.9 pCi/L
Placer County24 of 332837.4%1.1 pCi/L
Alameda County25 of 334786.7%0.7 pCi/L
Marin County26 of 33956.3%0.8 pCi/L
San Bernardino County27 of 331784.5%0.7 pCi/L
Orange County28 of 334313.9%0.7 pCi/L
San Francisco County29 of 332462.8%0.5 pCi/L
San Diego County30 of 336922.6%0.2 pCi/L
Yolo County31 of 33482.1%0.9 pCi/L
Riverside County32 of 332261.3%0.6 pCi/L
San Bernardino County ten-year laboratory totals, against California's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestCalifornia, pooledChange from the row before
2008 to 20171784.5%0.7 pCi/L10.1 pCi/L10.3%+0.3 points
2007 to 20161914.2%0.7 pCi/L35.5 pCi/L10.6%−0.1 points
2006 to 20151634.3%0.8 pCi/L35.5 pCi/L10.6%+0.6 points
2005 to 20141623.7%0.8 pCi/L35.5 pCi/L10.0%First on file

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

San Bernardino County, State data

California's own radon test data

Measured

What California's own agencies publish about radon tests in San Bernardino County, with their period. These are not CDC's figures and are never added to them.

MeasuredState figures, not CDC's

What the Nevada Radon Education Program reports for the ZIP codes in San Bernardino County

The Nevada Radon Education Program publishes its figures by ZIP code, not by county. These are the ZIP code that lie wholly or partly in San Bernardino County, each with the state's own figures for it. Period: 1989-2015.

ZIP codes in San Bernardino County
ZIP codeWhat the state reports
89019average 2.2 pCi/L
  • NBMG says the results are based on independently tested homes, not scientific sampling.
  • The service publishes an average for each ZIP code but no count of tests.
  • Site specific testing is the only way to determine local radon concentrations.
  • A ZIP code that crosses the county line is listed whole; its figures cover all of it.

Measured: Nevada Radon Education Program data, 1989-2015.

San Bernardino County, Geology

The ground under San Bernardino County

Predicted

Most of the ground under San Bernardino County is one class on USGS's geologic map: 84.3% of its land is low radon potential, with 15.7% moderate. The map puts 82.8% of San Bernardino County in the area it calls Mojave Desert and 8.4% in Basin and Range, with 2 smaller areas beside them. USGS gives the first a radon index of 8, in the low band (5 to 8), and the second 9, in the moderate band (9 to 11).

USGS's geologic areas under San Bernardino County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Mojave DesertPrecambrian and Paleozoic metamorphosed and unmetamorphosed sedimentary rocks, Mesozoic and Tertiary intrusive rocks, Tertiary sedimentary and volcanic rocks, and significant eolian deposits.Low882.8%
Basin and RangePrecambrian metamorphic rocks, late Precambrian and Paleozoic metamorphosed and unmetamorphosed sedimentary rocks, Mesozoic and Tertiary intrusive rocks, and Tertiary sedimentary and volcanic rocks.Moderate98.4%
Transverse RangesPrecambrian metamorphic rocks and Mesozoic granitic rocks, and the western part is underlain by Cretaceous to Pliocene marine sedimentary rocks.Moderate97.3%
Peninsular RangesGranite, metasedimentary and metavolcanic rocks, marine sedimentary rocks, and coastal sediments.Low71.5%

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

San Bernardino County beside the ground around it

Across California 0.1% of the land is rated high; none of San Bernardino County's is. Of the 8 counties that border it, 1 has more high-potential ground, Inyo County the most at 1.0%.

Share of land by USGS radon potential: San Bernardino County, the 8 counties bordering it and California
AreaEPA zoneLow potentialModerate potentialHigh potential
San Bernardino CountyZone 284.3%15.7%None
Riverside CountyZone 295.8%4.2%None
Clark County, NVZone 362.3%37.7%None
Los Angeles CountyZone 254.8%44.5%None
Orange CountyZone 399.5%NoneNone
Mohave County, AZZone 256.5%43.5%None
Inyo CountyZone 2None99.0%1.0%
La Paz County, AZZone 2100%NoneNone
Kern CountyZone 244.8%55.2%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

San Bernardino County, Local resources

Radon testing and mitigation in San Bernardino 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

San Bernardino County, Questions

Questions about radon in San Bernardino County

Are radon levels high in San Bernardino County?

Over the 2008 to 2017 laboratory totals, 4.5% of the radon tests reported to CDC for San Bernardino County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.7 pCi/L. Of 33 California counties with 30 or more tests for the same period, 26 reported a higher share; pooled, the state comes to 10.3%.

Which counties border San Bernardino County?

San Bernardino County borders 8 counties: Riverside County, CA, Clark County, NV, Los Angeles County, CA, Orange County, CA, Mohave County, AZ, Inyo County, CA, La Paz County, AZ and Kern County, CA.

Products

San Bernardino County, Products

Testing a home in San Bernardino County

In San Bernardino County, 4.5% of 178 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 San Bernardino County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for San Bernardino County homes, compared

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San Bernardino County, Bordering counties

Counties bordering San Bernardino County

Calculated by Radon411

San Bernardino County, Cities and towns

Cities and towns in San Bernardino County

The Census Bureau estimates 2,224,091 residents in San Bernardino County for July 1, 2025, 40,891 more than in 2020 (+1.9%). That works out to 111 people per square mile of land. No town dominates: San Bernardino, the largest, has 222,044 residents, 10.0% of the total. Together its 24 incorporated places hold 86.5% of those residents; the other 13.5% live outside any of them. Reported testing is thin here: 178 tests over 2008 to 2017, or 0.1 for every 1,000 residents (2025 estimate), where California as a whole comes to 0.2.

From San Bernardino to Needles, CDC publishes no figure by town: each reads San Bernardino County's.

The 12 largest cities and towns in San Bernardino County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
San Bernardino222,044Level10.0%
Fontana221,223+5.8%9.9%
Ontario187,013+6.4%8.4%
Rancho Cucamonga177,856+1.8%8.0%
Victorville141,395+5.0%6.4%
Rialto106,554+2.5%4.8%
Hesperia102,605+2.7%4.6%
Chino96,957+6.0%4.4%
Upland79,446+0.5%3.6%
Chino Hills77,519−1.2%3.5%
Apple Valley75,247−0.8%3.4%
Redlands74,128+1.2%3.3%
  • Highland
  • Yucaipa
  • Colton
  • Adelanto
  • Montclair
  • Twentynine Palms
  • Loma Linda
  • Barstow
  • Yucca Valley
  • Grand Terrace
  • Big Bear Lake
  • Needles

24 incorporated places, 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).

San Bernardino County, Homes

Homes in San Bernardino County

Of San Bernardino County's 738,535 homes, 70% are detached houses, against 57% across California; 14% are in buildings of five or more homes. Half of its homes were built before 1983, close to California's 1976: 18% date from before 1960 and 21% from 2000 or later. 62% 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 San Bernardino County, California, 2019 to 2023
HomesSan Bernardino CountyCalifornia
Housing units738,53514,532,683
Detached houses70%57%
In buildings of 5 or more14%24%
Mobile homes6%4%
Built before 196018%27%
Built since 200021%18%
Middle year built19831976
Owner-occupied62%56%

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