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Radon Levels in San Luis Obispo County, California

EPA puts San Luis Obispo County in Zone 2, its middle radon zone, and most reported tests there come back low, though 12.5% of 80 (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

How to test this homeFind a certified tester

  • Share at 4+ pCi/L

    12.5%

    2.2 pts above CA

    San Luis Obispo
    12.5%
    California
    10.3%

    80 tests, 2008 to 2017

  • Median result

    1.0pCi/L

    Below action level

    San Luis Obispo
    1.0 pCi/L
    EPA
    4.0 pCi/L

    Midpoint of the tests, 2008 to 2017

  • Tests reported

    80

    24th of 33 by tests

    San Luis Obispo
    80
    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

    13 of 33

    Middle half

    San Luis Obispo
    12.5%
    El Dorado
    30.3%

    By share, of 33 with 30+ tests

Read a result for San Luis Obispo County

Starts at San Luis Obispo County's median, 1.0 pCi/L

1.0pCi/L

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

EPA’s reading of 1.0 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 Luis Obispo County's median reported result, 2008 to 2017.

Interpret this reading

The data

San Luis Obispo County, At a glance

San Luis Obispo County at a glance

Predicted: EPA radon zone

EPA Zone 2: moderate predicted potential

San Luis Obispo 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 San Luis Obispo County, 2008 to 2017, laboratory

Reported results by concentration band, San Luis Obispo County, 2008 to 2017, laboratory
Under 2 pCi/L: 71%2 to 4 pCi/L: 16%4 pCi/L and above: 13%

Of 80 pre-mitigation tests reported to CDC, not homes in this area.

Reported results by concentration band, San Luis Obispo County, 2008 to 2017, laboratory: data table
Result bandTests MeasuredShare Measured
Under 2 pCi/L5771.3%
2 to 4 pCi/L1316.3%
4 pCi/L and above1012.5%
What these figures count

These are the 80 tests reported to CDC for San Luis Obispo 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 Luis Obispo County, Compared

San Luis Obispo County radon figures, compared

Calculated by Radon411

12.5% of its 80 tests over the 2008 to 2017 laboratory totals were at or above 4 pCi/L. That is 2.2 points above the 10.3% pooled from 56 California counties.

Ordered from highest share down, it comes 13th of 33 California counties with 30 or more tests for the same period. Nationally, every county with a figure for the same period pools to 35.7%; San Luis Obispo County sits 23.2 points below it.

Next door, the shares run from 11.6% in Kern County to 17.6% in Santa Barbara County, with Kern County below San Luis Obispo County. Zone 2 on EPA's map (predicted average between 2 and 4 pCi/L) and a 12.5% share point the same way here.

Half the tests came in under 1.0 pCi/L and half over it; the single highest reached 10.2 pCi/L. The rest split 71.3% under 2 pCi/L and 16.3% from 2 to 4 (California: 76.8% and 12.9%).

CDC's ten-year totals for San Luis Obispo County went from 720 tests (2005 to 2014) to 80 (2008 to 2017), the share going from 6.7% to 12.5%.

San Luis Obispo County against California, the United States and nearby counties, 2008 to 2017, laboratory
AreaTestsAt or above 4 pCi/LMedianDifference from San Luis Obispo County
San Luis Obispo County8012.5%1.0 pCi/LThis county
California, pooled56 counties, pooled9,41510.3%Not pooled−2.2 points
United States, pooled2,661 counties, pooled2,013,54435.7%Not pooled+23.2 points
El Dorado Countyhighest in the state27430.3%1.6 pCi/L+17.8 points
Sonoma Countylowest in the state1310.8%0.5 pCi/L−11.7 points
Santa Barbara County, CAborders it42117.6%1.2 pCi/L+5.1 points
Monterey County, CAborders it8714.9%0.8 pCi/L+2.4 points
Kern County, CAborders it12111.6%1.8 pCi/L−0.9 points
Kings County, CAborders it20.0%1.7 pCi/L−12.5 points
Where San Luis Obispo County's reported results fell, 2008 to 2017, laboratory, beside California and the United States
ResultSan Luis Obispo County testsSan Luis Obispo County shareCalifornia shareU.S. shareAgainst California
Under 2 pCi/L5771.3%76.8%39.6%−5.5 points
2 to 4 pCi/L1316.3%12.9%24.7%+3.4 points
4 pCi/L and above1012.5%10.3%35.7%+2.2 points
San Luis Obispo 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
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
Madera County12 of 333414.7%1.4 pCi/L
San Luis Obispo County13 of 338012.5%1.0 pCi/L
Ventura County14 of 3333511.9%1.0 pCi/L
Kern County15 of 3312111.6%1.8 pCi/L
Butte County16 of 333511.4%0.8 pCi/L
Fresno County17 of 3310011.0%1.5 pCi/L
Napa County18 of 335710.5%0.9 pCi/L
San Luis Obispo County ten-year laboratory totals, against California's pooled share
PeriodTestsAt or above 4 pCi/LMedianHighestCalifornia, pooledChange from the row before
2008 to 20178012.5%1.0 pCi/L10.2 pCi/L10.3%+4.3 points
2007 to 2016738.2%1.0 pCi/L9.6 pCi/L10.6%−1.0 points
2006 to 2015879.2%1.1 pCi/L9.6 pCi/L10.6%+2.5 points
2005 to 20147206.7%0.6 pCi/L20.2 pCi/L10.0%First on file

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

San Luis Obispo County, Geology

The ground under San Luis Obispo County

Predicted

USGS's geologic map puts all of San Luis Obispo County's mapped land in one class: moderate radon potential. All of it lies in the area the map calls Southern Coast Ranges, to which USGS gives a radon index of 9, in the moderate band (9 to 11).

USGS's geologic areas under San Luis Obispo County
AreaThe rock, in USGS's wordsPotentialRadon indexShare of land
Southern Coast RangesMetamorphosed marine sedimentary rocks, ultramafic rocks, Triasic metamorphic rocks, Mesozoic granitic rocks, and a series of fault-bounded linear basins in which Teriary marine and continental sedimentary rocks were deposited.Moderate999.7%

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

San Luis Obispo County beside the ground around it

Across California 0.1% of the land is rated high; none of San Luis Obispo County's is. Of the 4 counties that border it, 1 has more moderate-potential ground, Monterey County the most at 100%.

Share of land by USGS radon potential: San Luis Obispo County, the 4 counties bordering it and California
AreaEPA zoneLow potentialModerate potentialHigh potential
San Luis Obispo CountyZone 2None99.7%None
Santa Barbara CountyZone 16.9%92.7%None
Kings CountyZone 374.8%25.2%None
Kern CountyZone 244.8%55.2%None
Monterey CountyZone 2None100%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 Luis Obispo County, Local resources

Radon testing and mitigation in San Luis Obispo 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 Luis Obispo County, Questions

Questions about radon in San Luis Obispo County

Are radon levels high in San Luis Obispo County?

Over the 2008 to 2017 laboratory totals, 12.5% of the radon tests reported to CDC for San Luis Obispo County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.0 pCi/L. Of 33 California counties with 30 or more tests for the same period, 12 reported a higher share; pooled, the state comes to 10.3%.

Which counties border San Luis Obispo County?

San Luis Obispo County borders 4 counties: Santa Barbara County, Kings County, Kern County and Monterey County.

Products

San Luis Obispo County, Products

Testing a home in San Luis Obispo County

In San Luis Obispo County, 12.5% of 80 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 Luis Obispo County; a long-term test tells the year-round average.

Test kits and monitors3

See every kit and monitor

Best radon monitors for San Luis Obispo County homes, compared

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San Luis Obispo County, Bordering counties

Counties bordering San Luis Obispo County

Calculated by Radon411

San Luis Obispo County, Cities and towns

Cities and towns in San Luis Obispo County

San Luis Obispo County's population has barely moved since 2020: 282,367 residents on July 1, 2025 against 282,257 then, by the Census Bureau's estimates. That works out to 86 people per square mile of land. No town dominates: San Luis Obispo, the largest, has 50,636 residents, 17.9% of the total. Together its 7 incorporated places hold 57.0% of those residents; the other 43.0% live outside any of them. CDC's 80 reported tests for 2008 to 2017 work out to 0.3 per 1,000 residents (2025 estimate), close to California's 0.2.

From San Luis Obispo to Pismo Beach, CDC publishes no figure by town: each reads San Luis Obispo County's.

The cities and towns in San Luis Obispo County by residents, July 1, 2025
PlaceResidentsSince 2020Share of residents
San Luis Obispo50,636+7.3%17.9%
El Paso de Robles (Paso Robles)31,626+0.4%11.2%
Atascadero29,464−0.9%10.4%
Arroyo Grande18,123−1.7%6.4%
Grover Beach12,456−1.7%4.4%
Morro Bay10,613−1.3%3.8%
Pismo Beach7,911−1.8%2.8%

7 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 Luis Obispo County, Homes

Homes in San Luis Obispo County

Of San Luis Obispo County's 124,871 homes, 68% are detached houses, against 57% across California; 10% are in buildings of five or more homes. Half of its homes were built before 1983, close to California's 1976: 16% date from before 1960 and 23% 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 Luis Obispo County, California, 2019 to 2023
HomesSan Luis Obispo CountyCalifornia
Housing units124,87114,532,683
Detached houses68%57%
In buildings of 5 or more10%24%
Mobile homes8%4%
Built before 196016%27%
Built since 200023%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.