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Radon Levels in Riverside County, California

EPA puts Riverside County in Zone 2, its middle radon zone, and most reported tests there come back low, though 1.3% of 226 (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

    1.3%

    9.0 pts below CA

    Riverside
    1.3%
    California
    10.3%

    226 tests, 2008 to 2017

  • Median result

    0.6pCi/L

    Below action level

    Riverside
    0.6 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    226

    14th of 33 by tests

    Riverside
    226
    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

    32 of 33

    Lowest quarter

    Riverside
    1.3%
    El Dorado
    30.3%

    By share, of 33 with 30+ tests

Read a result for Riverside County

Starts at Riverside County's median, 0.6 pCi/L

0.6pCi/L

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

EPA’s reading of 0.6 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. Riverside County's median reported result, 2008 to 2017.

Interpret this reading

The data

Riverside County, At a glance

Riverside County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

Riverside 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 96% of the county's area

Predicted: EPA Map of Radon Zones

Measured: tests reported to CDC

Radon tests reported for Riverside County, 2008 to 2017, laboratory

Reported results by concentration band, Riverside County, 2008 to 2017, laboratory
Under 2 pCi/L: 96%2 to 4 pCi/L: 3%4 pCi/L and above: 1%

Of 226 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, Riverside County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L21695.6%
2 to 4 pCi/L73.1%
4 pCi/L and above31.3%
What these figures count

These are the 226 tests reported to CDC for Riverside 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

Riverside County, Compared

Riverside County radon figures, compared

Calculated by Radon411

Only 3 of 226 radon tests reported for Riverside County over the 2008 to 2017 laboratory totals reached 4 pCi/L (1.3%). The median result, 0.6 pCi/L, sits below 2, well under EPA's 4 pCi/L action level, and the top reported result was 11.2 pCi/L.

Across 56 California counties pooled together, 10.3% of tests reached that level, so Riverside County runs 9.0 points below its state. Against the national pool of 35.7%, the gap is 34.4 points lower. Its place in the state: 32nd 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 Riverside County (predicted average between 2 and 4 pCi/L): 1.3% of them reached 4 pCi/L, fewer than that label suggests. Of 3 neighbours with a figure, all 3 reported a larger share at or above 4 pCi/L; the spread is 2.6% (San Diego County) to 4.5% (San Bernardino County).

Below the action level, 216 tests (95.6%) came in under 2 pCi/L, against 76.8% statewide, and 7 tests (3.1%) fell between 2 and 4, against 12.9% statewide. USGS geology rates 96% of the county's land low radon potential.

CDC's ten-year totals for Riverside County went from 242 tests (2005 to 2014) to 226 (2008 to 2017), the share going from 0.8% to 1.3%.

Riverside County against California, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from Riverside County
Riverside County2261.3%0.6 pCi/LThis county
California, pooled56 counties, pooled9,41510.3%Not pooled+9.0 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+34.4 points
El Dorado Countyhighest in the state27430.3%1.6 pCi/L+29.0 points
Sonoma Countylowest in the state1310.8%0.5 pCi/L−0.5 points
San Bernardino County, CAborders it1784.5%0.7 pCi/L+3.2 points
Orange County, CAborders it4313.9%0.7 pCi/L+2.6 points
San Diego County, CAborders it6922.6%0.2 pCi/L+1.3 points
Imperial County, CAborders it110.0%0.6 pCi/L−1.3 points
Where Riverside County's reported results fell, 2008 to 2017, laboratory, beside California and the United States
ResultRiverside County testsRiverside County shareCalifornia shareU.S. shareAgainst California
Under 2 pCi/L21695.6%76.8%39.6%+18.8 points
2 to 4 pCi/L73.1%12.9%24.7%−9.8 points
4 pCi/L and above31.3%10.3%35.7%−9.0 points
Riverside 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
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
Sonoma County33 of 331310.8%0.5 pCi/L
Riverside County ten-year laboratory totals, against California's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestCalifornia, pooledChange from the row before
2008 to 20172261.3%0.6 pCi/L11.2 pCi/L10.3%+0.1 points
2007 to 20162421.2%0.6 pCi/L11.2 pCi/L10.6%Level
2006 to 20152451.2%0.5 pCi/L11.2 pCi/L10.6%+0.4 points
2005 to 20142420.8%0.5 pCi/L11.2 pCi/L10.0%First on file

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

Riverside County, Geology

The ground under Riverside County

Predicted

Most of the ground under Riverside County is one class on USGS's geologic map: 95.8% of its land is low radon potential, with 4.2% moderate. The map puts 53.8% of Riverside County in the area it calls Mojave Desert and 32.3% in Peninsular Ranges, with 2 smaller areas beside them. USGS gives the first a radon index of 8 and the second 7, both in the low band (5 to 8).

USGS's geologic areas under Riverside 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.Low853.8%
Peninsular RangesGranite, metasedimentary and metavolcanic rocks, marine sedimentary rocks, and coastal sediments.Low732.3%
Colorado DesertPleistocene to Holocene marine and (mostly) nonmarine gravel, sand, silt, and clay deposits.Low89.6%
Transverse RangesPrecambrian metamorphic rocks and Mesozoic granitic rocks, and the western part is underlain by Cretaceous to Pliocene marine sedimentary rocks.Moderate94.2%

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

Riverside County beside the ground around it

Across California 0.1% of the land is rated high; none of Riverside County's is. Of the 5 counties that border it, 1 has more moderate-potential ground, San Bernardino County the most at 15.7%.

Share of land by USGS radon potential: Riverside County, the 5 counties bordering it and California
AreaEPA zoneLow potentialModerate potentialHigh potential
Riverside CountyZone 295.8%4.2%None
San Diego CountyZone 399.5%NoneNone
Imperial CountyZone 3100%NoneNone
San Bernardino CountyZone 284.3%15.7%None
Orange CountyZone 399.5%NoneNone
La Paz County, AZZone 2100%NoneNone
California58 counties, pooled by land areaVaries57.2%42.6%0.1%

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

Local help

Riverside County, Local resources

Radon testing and mitigation in Riverside 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

Riverside County, Questions

Questions about radon in Riverside County

Are radon levels high in Riverside County?

Over the 2008 to 2017 laboratory totals, 1.3% of the radon tests reported to CDC for Riverside County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 0.6 pCi/L. Of 33 California counties with 30 or more tests for the same period, 31 reported a higher share; pooled, the state comes to 10.3%.

Which counties border Riverside County?

Riverside County borders 5 counties: San Diego County, CA, Imperial County, CA, San Bernardino County, CA, Orange County, CA and La Paz County, AZ.

Products

Riverside County, Products

Testing a home in Riverside County

In Riverside County, 1.3% of 226 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 Riverside County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for Riverside County homes, compared

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Riverside County, Bordering counties

Counties bordering Riverside County

Calculated by Radon411

Riverside County, Cities and towns

Cities and towns in Riverside County

The Census Bureau estimates 2,544,916 residents in Riverside County for July 1, 2025, 120,470 more than in 2020 (+5.0%). That works out to 353 people per square mile of land. No town dominates: Riverside, the largest, has 323,057 residents, 12.7% of the total. Together its 28 incorporated places hold 83.0% of those residents; the other 17.0% live outside any of them. Reported testing is thin here: 226 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 Riverside to Indian Wells, CDC publishes no figure by town: each reads Riverside County's.

The 12 largest cities and towns in Riverside County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
Riverside323,057+2.4%12.7%
Moreno Valley214,263+2.6%8.4%
Corona161,734+2.7%6.4%
Menifee118,592+14.9%4.7%
Temecula114,865+4.4%4.5%
Murrieta114,124+2.7%4.5%
Jurupa Valley107,311+1.9%4.2%
Indio94,269+5.4%3.7%
Hemet93,649+4.2%3.7%
Perris83,237+5.6%3.3%
Lake Elsinore75,067+6.4%2.9%
Eastvale70,594+0.8%2.8%
  • Beaumont
  • San Jacinto
  • Palm Desert
  • Cathedral City
  • Coachella
  • Palm Springs
  • La Quinta
  • Wildomar
  • Desert Hot Springs
  • Banning
  • Norco
  • Rancho Mirage
  • Blythe
  • Canyon Lake
  • Calimesa
  • Indian Wells

28 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).

Riverside County, Homes

Homes in Riverside County

Of Riverside County's 860,042 homes, 69% are detached houses, against 57% across California; 12% are in buildings of five or more homes. Much of Riverside County is recent building: 35% of its homes have gone up since 2000 and the middle year built is 1990, against 1976 for California. 69% 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 Riverside County, California, 2019 to 2023
HomesRiverside CountyCalifornia
Housing units860,04214,532,683
Detached houses69%57%
In buildings of 5 or more12%24%
Mobile homes9%4%
Built before 19609%27%
Built since 200035%18%
Middle year built19901976
Owner-occupied69%56%

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