Short-term kitFirst Alert
RD1 short-term charcoal radon test kit
- Lab fee included
Method: Charcoal
In home: 2 to 4 days
Locations and reports
Radon Levels in Siskiyou County, California
EPA puts Siskiyou County in Zone 3, its lowest radon zone, and only 8 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
10.0%
Josephine County
- Josephine
- 10.0%
- Jackson
- 5.3%
3 of 8 neighbours have 30+ tests, 2008 to 2017
Nearest county
11.4%
Butte County, 142 miles
- Butte
- 11.4%
- California
- 10.3%
Share at 4+ pCi/L, 35 tests, 2008 to 2017
Ground above low
5.6%
37.1 pts below California
- Siskiyou
- 5.6%
- California
- 42.7%
Share of land USGS rates moderate or high potential
Tests reported
11
Too few for a share
- Siskiyou
- 11
- Needed
- 30
2005 to 2014, laboratory
EPA radon zone
Zone 3
Lower potential
- 1
- 2
- Zone 3
1 highest, 3 lowest
EPA predicts under 2 pCi/L indoors
Read a result for Siskiyou 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
Siskiyou County, At a glance
Siskiyou County at a glance
Predicted: EPA radon zone
EPA Zone 3: lower predicted potential
USGS geologic potential: Low across 94% of the county's area
Predicted: EPA Map of Radon Zones
Measured: tests reported to CDC
Radon tests reported for Siskiyou County, 2008 to 2017, laboratory
CDC holds 8 reported tests for Siskiyou County over the 2008 to 2017 laboratory totals, with a median of 1.1 pCi/L: too few to describe a county (Radon411 reads a share from 30 tests up). Siskiyou County beside the counties around it is how this page reads it.
What these figures count
Only 8 tests were reported to CDC for Siskiyou 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).
Siskiyou County, Compared
Siskiyou County radon figures, compared
Calculated by Radon411CDC's largest figure for Siskiyou County rests on 11 tests over the 2005 to 2014 laboratory totals, 2 of them at or above 4 pCi/L, so each test moves its share by 9.1 points and no rank or comparison is drawn from it. Results reached as high as 8.0 pCi/L, with a middle value of 1.7 pCi/L.
Of the counties bordering it, 3 have a figure over the 2008 to 2017 laboratory totals: Josephine County, OR reported the largest share at or above 4 pCi/L, 10.0%, and Jackson County, OR the smallest, 5.3%, with Klamath County, OR at 5.3% between. Farther out, Butte County (142 miles away) at 11.4%, Nevada County (184 miles away) at 25.0% and Placer County (199 miles away) at 7.4% 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 Siskiyou County in Zone 3, its lowest label: a predicted county average under 2 pCi/L. USGS geology rates 94% of the county's land low radon potential.
Pooled shares: Radon411's sum of CDC's county counts for one period.
Siskiyou County, Geology
The ground under Siskiyou County
PredictedMost of the ground under Siskiyou County is one class on USGS's geologic map: 94.4% of its land is low radon potential, with 5.6% moderate. The map puts 51.2% of Siskiyou County in the area it calls Klamath Mountains and 43.2% in Cascade Range, with one smaller area beside them. USGS gives the first a radon index of 6 and the second 8, both in the low band (5 to 8).
| Area | The rock, in USGS's words | Potential | Radon index | Share of land |
|---|---|---|---|---|
| Klamath Mountains | Metasedimentary and ultramafic metavolcanic rocks, and basalt. | Low | 6 | 51.2% |
| Cascade Range | Upper Tertiary and Quaternary extrusive rocks, mainly basalt and lesser andesite and rhyolite. | Low | 8 | 43.2% |
| Northern Basin and Range | Precambrian metamorphic rocks, late Precambrian and Paleozoic metamorphosed and unmetamorphosed sedimentary rocks, Mesozoic and Tertiary intrusive rocks, and Tertiary sedimentary and volcanic rocks. | Moderate | 9 | 5.6% |
Names, descriptions and indexes: U.S. Geological Survey, Geologic Radon Potential Map (2025). Shares: Radon411, from the map cut to the boundary.
Siskiyou County beside the ground around it
Across California 0.1% of the land is rated high; none of Siskiyou County's is. Of the 8 counties that border it, 2 have more moderate-potential ground, Klamath County, OR the most at 71.6%.
The map rates the ground, not the air in any home.
Local help
Siskiyou County, Local resources
Radon testing and mitigation in Siskiyou 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
Siskiyou County, Questions
Questions about radon in Siskiyou County
Are radon levels high in Siskiyou County?
Over the 2008 to 2017 laboratory totals, 25.0% of the radon tests reported to CDC for Siskiyou County, California were at or above 4 pCi/L, and the median reported pre-mitigation result was 1.1 pCi/L. Of the counties bordering it, 3 have a figure over the 2008 to 2017 laboratory totals: Josephine County, OR reported the largest share at or above 4 pCi/L, 10.0%, and Jackson County, OR the smallest, 5.3%, with Klamath County, OR at 5.3% between.
Which counties border Siskiyou County?
Siskiyou County borders 8 counties: Shasta County, CA, Trinity County, CA, Jackson County, OR, Del Norte County, CA, Josephine County, OR, Humboldt County, CA, Modoc County, CA and Klamath County, OR.
Products
Siskiyou County, Products
Testing a home in Siskiyou County
No CDC figure names Siskiyou County; the nearest county with one, Butte County (142 miles away), reported 11.4% 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. Zone 3 is the lowest label, yet homes at or above 4 pCi/L occur in every zone: a short-term kit (2 to 90 days) is the quick first check in Siskiyou County.
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
View Plus radon and air quality monitor
- C-NRPP 2024/25: Approved
- Battery
- Wi-Fi, Bluetooth
- Screen, app
Method: Alpha spectrometry
- See every kit and monitor Test kits and monitors
Test kits and monitors: 1 of 3
Explore
Siskiyou County, Bordering counties
Counties bordering Siskiyou County
Calculated by Radon411- Radon levels in Shasta County, CAEPA zone 3
21.7%at or above 4 pCi/L
Median 2.0 pCi/L · 23 tests
- Radon levels in Humboldt County, CAEPA zone 3
20.0%at or above 4 pCi/L
Median 1.3 pCi/L · 20 tests
- Radon levels in Josephine County, OREPA zone 3
10.0%at or above 4 pCi/L
Median 0.7 pCi/L · 30 tests
- Radon levels in Jackson County, OREPA zone 3
5.3%at or above 4 pCi/L
Median 1.0 pCi/L · 113 tests
- Radon levels in Klamath County, OREPA zone 2
5.3%at or above 4 pCi/L
Median 0.4 pCi/L · 38 tests
- Radon levels in Del Norte County, CAEPA zone 3
0.0%at or above 4 pCi/L
Median 0.1 pCi/L · 1 test
- Radon levels in Trinity County, CAEPA zone 3
No CDC figure for 2008 to 2017; its page reads it against its own neighbours.
- Radon levels in Modoc County, CAEPA zone 3
No CDC figure for 2008 to 2017; its page reads it against its own neighbours.
Siskiyou County, Cities and towns
Cities and towns in Siskiyou County
About 42,013 people live in Siskiyou County by the Census Bureau's estimate for July 1, 2025, 1,970 fewer than in 2020 (−4.5%). Spread over its land, that is 6.7 people to the square mile. No town dominates: Yreka, the largest, has 7,714 residents, 18.4% of the total. Together its 9 incorporated places hold 45.4% of those residents; the other 54.6% live outside any of them. CDC's 11 reported tests for 2005 to 2014 work out to 0.3 per 1,000 residents (2025 estimate), close to California's 0.3.
From Yreka to Etna, CDC publishes no figure by town: each reads Siskiyou County's.
| Place | Residents | Since 2020 | Share of residents |
|---|---|---|---|
| Yreka | 7,714 | −1.2% | 18.4% |
| Mount Shasta | 3,071 | −4.6% | 7.3% |
| Weed | 2,603 | −9.0% | 6.2% |
| Dunsmuir | 1,587 | −6.7% | 3.8% |
| Montague | 1,157 | −5.2% | 2.8% |
| Tulelake | 833 | −7.0% | 2.0% |
| Dorris | 803 | −6.2% | 1.9% |
| Fort Jones | 659 | −6.1% | 1.6% |
| Etna | 631 | −6.2% | 1.5% |
9 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).
Siskiyou County, Homes
Homes in Siskiyou County
Of Siskiyou County's 23,066 homes, 74% are detached houses, against 57% across California; 12% are mobile homes. Half of its homes were built before 1976, close to California's 1976: 29% date from before 1960 and 14% from 2000 or later. 70% 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 | Siskiyou County | California |
|---|---|---|
| Housing units | 23,066 | 14,532,683 |
| Detached houses | 74% | 57% |
| In buildings of 5 or more | 6% | 24% |
| Mobile homes | 12% | 4% |
| Built before 1960 | 29% | 27% |
| Built since 2000 | 14% | 18% |
| Middle year built | 1976 | 1976 |
| Owner-occupied | 70% | 56% |
Census Bureau, American Community Survey, 2019 to 2023: estimates from a sample of homes, looser for a small place. Shares by Radon411.