California Cities Ranked by Indoor Radon Levels

Measured averages from Airthings devices across California, USA. Action level: 4 pCi/L — the threshold at which remediation is recommended.

Mammoth Lakes has the highest measured indoor radon in California at 6.1 pCi/L, based on Airthings measurements across 376 cities.

Updated October 25, 2026

Highest city

6.1pCi/L

Mammoth Lakes

California city average

1.1pCi/L

across 376 cities

Above action level

6/ 376

cities

California Cities Ranked by Indoor Radon Levels
#	Location	Avg level	vs action level
1	Mammoth Lakes	6.1 pCi/L	1.5× over
2	Lake Arrowhead	6.0 pCi/L	1.5× over
3	Deer Park	5.9 pCi/L	1.5× over
4	Echo Park	5.5 pCi/L	1.4× over
5	Bishop	4.4 pCi/L	1.1× over
6	Alta Sierra	4.1 pCi/L	1.0× over
✓ Below EPA action level (4 pCi/L)
7	Atascadero	3.7 pCi/L	0.9× under
8	West Hills	3.7 pCi/L	0.9× under
9	South Lake Tahoe	3.6 pCi/L	0.9× under
10	Pomona	3.3 pCi/L	0.8× under
11	Fairfield	3.1 pCi/L	0.8× under
12	Brea	3.1 pCi/L	0.8× under
13	Mission Canyon	3.0 pCi/L	0.8× under
14	La Habra Heights	3.0 pCi/L	0.7× under
15	East Palo Alto	2.9 pCi/L	0.7× under
16	Alameda	2.8 pCi/L	0.7× under
17	Grass Valley	2.8 pCi/L	0.7× under
18	Truckee	2.7 pCi/L	0.7× under
19	Oildale	2.6 pCi/L	0.7× under
20	Woodland Hills	2.6 pCi/L	0.7× under
21	Dollar Point	2.5 pCi/L	0.6× under
22	Palos Verdes Estates	2.5 pCi/L	0.6× under
23	Sunnyside-Tahoe City	2.5 pCi/L	0.6× under
24	Nevada City	2.5 pCi/L	0.6× under
25	East Oakdale	2.5 pCi/L	0.6× under
26	Kings Beach	2.5 pCi/L	0.6× under
27	Hayward	2.4 pCi/L	0.6× under
28	Los Gatos	2.3 pCi/L	0.6× under
29	Twain Harte	2.3 pCi/L	0.6× under
30	Templeton	2.3 pCi/L	0.6× under
31	Lexington Hills	2.2 pCi/L	0.6× under
32	Scotts Valley	2.2 pCi/L	0.6× under
33	Tahoe Vista	2.2 pCi/L	0.6× under
34	Hidden Hills	2.2 pCi/L	0.6× under
35	Lathrop	2.2 pCi/L	0.6× under
36	Rancho Palos Verdes	2.2 pCi/L	0.6× under
37	Calabasas	2.2 pCi/L	0.5× under
38	Westlake Village	2.1 pCi/L	0.5× under
39	Felton	2.1 pCi/L	0.5× under
40	Tahoma	2.1 pCi/L	0.5× under
41	Minkler	2.1 pCi/L	0.5× under
42	Portola Valley	2.1 pCi/L	0.5× under
43	Fresno	2.1 pCi/L	0.5× under
44	Sherman Oaks	2.1 pCi/L	0.5× under
45	Simi Valley	2.0 pCi/L	0.5× under
46	Montecito	2.0 pCi/L	0.5× under
47	Arnold	2.0 pCi/L	0.5× under
48	Boulder Creek	2.0 pCi/L	0.5× under
49	Agoura	1.9 pCi/L	0.5× under
50	Saratoga	1.8 pCi/L	0.5× under
51	Woodside	1.8 pCi/L	0.5× under
52	Pasatiempo	1.8 pCi/L	0.5× under
53	Ramona	1.8 pCi/L	0.5× under
54	Summerland	1.8 pCi/L	0.4× under
55	Villa Park	1.8 pCi/L	0.4× under
56	North Fair Oaks	1.7 pCi/L	0.4× under
57	Ojai	1.7 pCi/L	0.4× under
58	Isla Vista	1.7 pCi/L	0.4× under
59	San Pedro	1.7 pCi/L	0.4× under
60	Loyola	1.6 pCi/L	0.4× under
61	La Habra	1.6 pCi/L	0.4× under
62	Santa Susana	1.6 pCi/L	0.4× under
63	Fair Oaks	1.6 pCi/L	0.4× under
64	Northridge	1.6 pCi/L	0.4× under
65	Universal City	1.6 pCi/L	0.4× under
66	Modesto	1.5 pCi/L	0.4× under
67	Chico	1.5 pCi/L	0.4× under
68	Orinda	1.5 pCi/L	0.4× under
69	Laguna	1.5 pCi/L	0.4× under
70	Menlo Park	1.5 pCi/L	0.4× under
71	Alturas	1.4 pCi/L	0.4× under
72	Santa Barbara	1.4 pCi/L	0.4× under
73	Culver City	1.4 pCi/L	0.4× under
74	Emeryville	1.4 pCi/L	0.4× under
75	Palo Alto	1.4 pCi/L	0.4× under
76	Parkway	1.4 pCi/L	0.4× under
77	Buena Vista	1.4 pCi/L	0.4× under
78	Alamo	1.4 pCi/L	0.4× under
79	Palm Springs	1.4 pCi/L	0.3× under
80	Corona	1.4 pCi/L	0.3× under
81	Rolling Hills Estates	1.3 pCi/L	0.3× under
82	East Richmond Heights	1.3 pCi/L	0.3× under
83	Indio	1.3 pCi/L	0.3× under
84	Agoura Hills	1.3 pCi/L	0.3× under
85	Malibu Beach	1.3 pCi/L	0.3× under
86	Mount Hermon	1.3 pCi/L	0.3× under
87	Sleepy Hollow	1.3 pCi/L	0.3× under
88	Mission Viejo	1.3 pCi/L	0.3× under
89	Canoga Park	1.3 pCi/L	0.3× under
90	Davis	1.3 pCi/L	0.3× under
91	Fullerton	1.3 pCi/L	0.3× under
92	Sunnyvale	1.3 pCi/L	0.3× under
93	Brentwood	1.3 pCi/L	0.3× under
94	Atherton	1.3 pCi/L	0.3× under
95	Placentia	1.3 pCi/L	0.3× under
96	Visalia	1.2 pCi/L	0.3× under
97	Chino Hills	1.2 pCi/L	0.3× under
98	East Foothills	1.2 pCi/L	0.3× under
99	Empire	1.2 pCi/L	0.3× under
100	Gold River	1.2 pCi/L	0.3× under
101	Los Altos Hills	1.2 pCi/L	0.3× under
102	North Hollywood	1.2 pCi/L	0.3× under
103	Vineyard	1.2 pCi/L	0.3× under
104	Monterey Park	1.1 pCi/L	0.3× under
105	Pleasant Hill	1.1 pCi/L	0.3× under
106	Campbell	1.1 pCi/L	0.3× under
107	Los Altos	1.1 pCi/L	0.3× under
108	Newark	1.1 pCi/L	0.3× under
109	Altadena	1.1 pCi/L	0.3× under
110	Anaheim	1.1 pCi/L	0.3× under
111	Piedmont	1.1 pCi/L	0.3× under
112	Rolling Hills	1.1 pCi/L	0.3× under
113	Poway	1.1 pCi/L	0.3× under
114	Glendale	1.1 pCi/L	0.3× under
115	Carmel Valley Village	1.1 pCi/L	0.3× under
116	Lincoln Village	1.1 pCi/L	0.3× under
117	Concord	1.1 pCi/L	0.3× under
118	Oceanside	1.1 pCi/L	0.3× under
119	Salinas	1.1 pCi/L	0.3× under
120	Corte Madera	1.0 pCi/L	0.3× under
121	Goleta	1.0 pCi/L	0.3× under
122	Malibu	1.0 pCi/L	0.3× under
123	Redwood City	1.0 pCi/L	0.3× under
124	Topanga	1.0 pCi/L	0.3× under
125	Castro Valley	1.0 pCi/L	0.3× under
126	East Pasadena	1.0 pCi/L	0.3× under
127	Danville	1.0 pCi/L	0.3× under
128	West Menlo Park	1.0 pCi/L	0.3× under
129	Carmel-by-the-Sea	1.0 pCi/L	0.3× under
130	Hacienda Heights	1.0 pCi/L	0.3× under
131	Orangevale	1.0 pCi/L	0.3× under
132	Van Nuys	1.0 pCi/L	0.3× under
133	Casa de Oro-Mount Helix	1.0 pCi/L	0.2× under
134	Crockett	1.0 pCi/L	0.2× under
135	Santa Clara	1.0 pCi/L	0.2× under
136	Clovis	1.0 pCi/L	0.2× under
137	Kensington	1.0 pCi/L	0.2× under
138	Los Serranos	1.0 pCi/L	0.2× under
139	Walnut	1.0 pCi/L	0.2× under
140	Cupertino	0.9 pCi/L	0.2× under
141	Yountville	0.9 pCi/L	0.2× under
142	Emerald Lake Hills	0.9 pCi/L	0.2× under
143	Hollywood	0.9 pCi/L	0.2× under
144	Santa Monica	0.9 pCi/L	0.2× under
145	Oak Park	0.9 pCi/L	0.2× under
146	Chatsworth	0.9 pCi/L	0.2× under
147	Ladera	0.9 pCi/L	0.2× under
148	Santa Venetia	0.9 pCi/L	0.2× under
149	Walnut Creek	0.9 pCi/L	0.2× under
150	Whittier	0.9 pCi/L	0.2× under
151	Home Gardens	0.9 pCi/L	0.2× under
152	South Pasadena	0.9 pCi/L	0.2× under
153	Century City	0.9 pCi/L	0.2× under
154	Sacramento	0.9 pCi/L	0.2× under
155	San Luis Obispo	0.9 pCi/L	0.2× under
156	Tustin	0.9 pCi/L	0.2× under
157	Ventura	0.9 pCi/L	0.2× under
158	Westwood, Los Angeles	0.9 pCi/L	0.2× under
159	Belvedere	0.9 pCi/L	0.2× under
160	Camarillo	0.9 pCi/L	0.2× under
161	Woodland	0.9 pCi/L	0.2× under
162	Belmont	0.8 pCi/L	0.2× under
163	Mill Valley	0.8 pCi/L	0.2× under
164	Moraga	0.8 pCi/L	0.2× under
165	Mountain View	0.8 pCi/L	0.2× under
166	San Juan Capistrano	0.8 pCi/L	0.2× under
167	Novato	0.8 pCi/L	0.2× under
168	Saranap	0.8 pCi/L	0.2× under
169	Silver Lake	0.8 pCi/L	0.2× under
170	Monte Sereno	0.8 pCi/L	0.2× under
171	San Marino	0.8 pCi/L	0.2× under
172	Yorba Linda	0.8 pCi/L	0.2× under
173	Cambrian Park	0.8 pCi/L	0.2× under
174	Diamond Bar	0.8 pCi/L	0.2× under
175	Elk Grove	0.8 pCi/L	0.2× under
176	Fairbanks Ranch	0.8 pCi/L	0.2× under
177	Tracy	0.8 pCi/L	0.2× under
178	Laguna Niguel	0.8 pCi/L	0.2× under
179	San Anselmo	0.8 pCi/L	0.2× under
180	Thousand Oaks	0.8 pCi/L	0.2× under
181	Beverly Hills	0.8 pCi/L	0.2× under
182	Fairfax	0.8 pCi/L	0.2× under
183	Fontana	0.8 pCi/L	0.2× under
184	Fremont	0.8 pCi/L	0.2× under
185	La Verne	0.8 pCi/L	0.2× under
186	Sausalito	0.8 pCi/L	0.2× under
187	Carmichael	0.8 pCi/L	0.2× under
188	Highlands-Baywood Park	0.8 pCi/L	0.2× under
189	Laguna Woods	0.8 pCi/L	0.2× under
190	Bonsall	0.8 pCi/L	0.2× under
191	Folsom	0.8 pCi/L	0.2× under
192	Lafayette	0.8 pCi/L	0.2× under
193	San Gabriel	0.8 pCi/L	0.2× under
194	Waldon	0.8 pCi/L	0.2× under
195	Fairview	0.8 pCi/L	0.2× under
196	Murrieta Hot Springs	0.8 pCi/L	0.2× under
197	Rancho Santa Fe	0.8 pCi/L	0.2× under
198	El Cerrito	0.7 pCi/L	0.2× under
199	La Crescenta-Montrose	0.7 pCi/L	0.2× under
200	San Carlos	0.7 pCi/L	0.2× under
201	Albany	0.7 pCi/L	0.2× under
202	Brisbane	0.7 pCi/L	0.2× under
203	Gilroy	0.7 pCi/L	0.2× under
204	Redlands	0.7 pCi/L	0.2× under
205	Roseville	0.7 pCi/L	0.2× under
206	Seven Trees	0.7 pCi/L	0.2× under
207	Stanford	0.7 pCi/L	0.2× under
208	Union City	0.7 pCi/L	0.2× under
209	Berkeley	0.7 pCi/L	0.2× under
210	Los Angeles	0.7 pCi/L	0.2× under
211	Moorpark	0.7 pCi/L	0.2× under
212	Pasadena	0.7 pCi/L	0.2× under
213	Petaluma	0.7 pCi/L	0.2× under
214	Westminster	0.7 pCi/L	0.2× under
215	Marina del Rey	0.7 pCi/L	0.2× under
216	Rocklin	0.7 pCi/L	0.2× under
217	San Leandro	0.7 pCi/L	0.2× under
218	Burlingame	0.7 pCi/L	0.2× under
219	Oxnard	0.7 pCi/L	0.2× under
220	Oxnard Shores	0.7 pCi/L	0.2× under
221	Rowland Heights	0.7 pCi/L	0.2× under
222	San Fernando	0.7 pCi/L	0.2× under
223	Benicia	0.7 pCi/L	0.2× under
224	Burbank	0.7 pCi/L	0.2× under
225	El Sobrante	0.7 pCi/L	0.2× under
226	Las Flores	0.7 pCi/L	0.2× under
227	Rancho Mirage	0.7 pCi/L	0.2× under
228	Sebastopol	0.7 pCi/L	0.2× under
229	Alum Rock	0.7 pCi/L	0.2× under
230	Del Mar	0.7 pCi/L	0.2× under
231	Hermosa Beach	0.7 pCi/L	0.2× under
232	Lomita	0.7 pCi/L	0.2× under
233	San Marcos	0.7 pCi/L	0.2× under
234	Santa Ana	0.7 pCi/L	0.2× under
235	Alondra Park	0.7 pCi/L	0.2× under
236	Aptos	0.7 pCi/L	0.2× under
237	Clayton	0.7 pCi/L	0.2× under
238	Ladera Ranch	0.7 pCi/L	0.2× under
239	Lucas Valley-Marinwood	0.7 pCi/L	0.2× under
240	San Joaquin Hills	0.7 pCi/L	0.2× under
241	Sonoma	0.7 pCi/L	0.2× under
242	Valley Center	0.7 pCi/L	0.2× under
243	Escondido	0.6 pCi/L	0.2× under
244	Morongo Valley	0.6 pCi/L	0.2× under
245	Del Aire	0.6 pCi/L	0.2× under
246	Inglewood	0.6 pCi/L	0.2× under
247	La Mesa	0.6 pCi/L	0.2× under
248	Ladera Heights	0.6 pCi/L	0.2× under
249	North Tustin	0.6 pCi/L	0.2× under
250	West Hollywood	0.6 pCi/L	0.2× under
251	Woodcrest	0.6 pCi/L	0.2× under
252	Carlsbad	0.6 pCi/L	0.2× under
253	Morgan Hill	0.6 pCi/L	0.2× under
254	San Ramon	0.6 pCi/L	0.2× under
255	Buena Park	0.6 pCi/L	0.2× under
256	Daly City	0.6 pCi/L	0.2× under
257	East San Gabriel	0.6 pCi/L	0.2× under
258	Livermore	0.6 pCi/L	0.2× under
259	San Jose	0.6 pCi/L	0.2× under
260	View Park-Windsor Hills	0.6 pCi/L	0.2× under
261	Bakersfield	0.6 pCi/L	0.1× under
262	El Granada	0.6 pCi/L	0.1× under
263	La Jolla	0.6 pCi/L	0.1× under
264	Portola Hills	0.6 pCi/L	0.1× under
265	San Rafael	0.6 pCi/L	0.1× under
266	La Canada Flintridge	0.6 pCi/L	0.1× under
267	Laguna Beach	0.6 pCi/L	0.1× under
268	Lincoln	0.6 pCi/L	0.1× under
269	Alhambra	0.6 pCi/L	0.1× under
270	Cerritos	0.6 pCi/L	0.1× under
271	Indian Wells	0.6 pCi/L	0.1× under
272	San Diego	0.6 pCi/L	0.1× under
273	Santa Cruz	0.6 pCi/L	0.1× under
274	West Sacramento	0.6 pCi/L	0.1× under
275	El Cajon	0.6 pCi/L	0.1× under
276	Milpitas	0.6 pCi/L	0.1× under
277	Vallejo	0.6 pCi/L	0.1× under
278	Foothill Ranch	0.6 pCi/L	0.1× under
279	Hillsborough	0.6 pCi/L	0.1× under
280	San Mateo	0.6 pCi/L	0.1× under
281	Stanton	0.6 pCi/L	0.1× under
282	Temple City	0.6 pCi/L	0.1× under
283	Antelope	0.6 pCi/L	0.1× under
284	Fallbrook	0.5 pCi/L	0.1× under
285	Larkfield-Wikiup	0.5 pCi/L	0.1× under
286	San Clemente	0.5 pCi/L	0.1× under
287	Saticoy	0.5 pCi/L	0.1× under
288	Pleasanton	0.5 pCi/L	0.1× under
289	Blackhawk	0.5 pCi/L	0.1× under
290	Irvine	0.5 pCi/L	0.1× under
291	Lake Forest	0.5 pCi/L	0.1× under
292	Lake San Marcos	0.5 pCi/L	0.1× under
293	Rossmoor	0.5 pCi/L	0.1× under
294	Trabuco Canyon	0.5 pCi/L	0.1× under
295	Boyle Heights	0.5 pCi/L	0.1× under
296	Dublin	0.5 pCi/L	0.1× under
297	Encinitas	0.5 pCi/L	0.1× under
298	Napa	0.5 pCi/L	0.1× under
299	Vacaville	0.5 pCi/L	0.1× under
300	East La Mirada	0.5 pCi/L	0.1× under
301	Oakland	0.5 pCi/L	0.1× under
302	San Francisco	0.5 pCi/L	0.1× under
303	Ashland	0.5 pCi/L	0.1× under
304	El Rio	0.5 pCi/L	0.1× under
305	Monrovia	0.5 pCi/L	0.1× under
306	Santa Rosa	0.5 pCi/L	0.1× under
307	Tamalpais-Homestead Valley	0.5 pCi/L	0.1× under
308	Richmond	0.5 pCi/L	0.1× under
309	San Antonio Heights	0.5 pCi/L	0.1× under
310	Healdsburg	0.5 pCi/L	0.1× under
311	Aliso Viejo	0.5 pCi/L	0.1× under
312	El Dorado Hills	0.5 pCi/L	0.1× under
313	Mira Loma	0.5 pCi/L	0.1× under
314	Torrance	0.5 pCi/L	0.1× under
315	Colma	0.5 pCi/L	0.1× under
316	Redondo Beach	0.5 pCi/L	0.1× under
317	Sierra Madre	0.5 pCi/L	0.1× under
318	Windsor	0.5 pCi/L	0.1× under
319	Cameron Park	0.4 pCi/L	0.1× under
320	Casa Conejo	0.4 pCi/L	0.1× under
321	Del Rey Oaks	0.4 pCi/L	0.1× under
322	Los Alamitos	0.4 pCi/L	0.1× under
323	Rancho Cucamonga	0.4 pCi/L	0.1× under
324	Strawberry	0.4 pCi/L	0.1× under
325	Lemon Grove	0.4 pCi/L	0.1× under
326	Orcutt	0.4 pCi/L	0.1× under
327	Huntington Beach	0.4 pCi/L	0.1× under
328	Vista	0.4 pCi/L	0.1× under
329	Claremont	0.4 pCi/L	0.1× under
330	Coronado	0.4 pCi/L	0.1× under
331	Gardena	0.4 pCi/L	0.1× under
332	Midway City	0.4 pCi/L	0.1× under
333	Temecula	0.4 pCi/L	0.1× under
334	Arden-Arcade	0.4 pCi/L	0.1× under
335	Chino	0.4 pCi/L	0.1× under
336	Guerneville	0.4 pCi/L	0.1× under
337	Mayflower Village	0.4 pCi/L	0.1× under
338	Santa Clarita	0.4 pCi/L	0.1× under
339	Costa Mesa	0.4 pCi/L	0.1× under
340	National City	0.4 pCi/L	0.1× under
341	Fountain Valley	0.4 pCi/L	0.1× under
342	Redwood Shores	0.4 pCi/L	0.1× under
343	Seacliff	0.4 pCi/L	0.1× under
344	Granite Bay	0.3 pCi/L	0.1× under
345	La Mirada	0.3 pCi/L	0.1× under
346	Manhattan Beach	0.3 pCi/L	0.1× under
347	North Glendale	0.3 pCi/L	0.1× under
348	El Segundo	0.3 pCi/L	0.1× under
349	Hawaiian Gardens	0.3 pCi/L	0.1× under
350	Millbrae	0.3 pCi/L	0.1× under
351	Montebello	0.3 pCi/L	0.1× under
352	Norco	0.3 pCi/L	0.1× under
353	Pacifica	0.3 pCi/L	0.1× under
354	Yucaipa	0.3 pCi/L	0.1× under
355	Lakewood	0.3 pCi/L	0.1× under
356	Long Beach	0.3 pCi/L	0.1× under
357	Orange	0.3 pCi/L	0.1× under
358	Palm Desert	0.3 pCi/L	0.1× under
359	Signal Hill	0.3 pCi/L	0.1× under
360	La Palma	0.3 pCi/L	0.1× under
361	South San Francisco	0.3 pCi/L	0.1× under
362	Lawndale	0.3 pCi/L	0.1× under
363	Pacific Grove	0.3 pCi/L	0.1× under
364	Arcadia	0.3 pCi/L	0.1× under
365	Valencia	0.3 pCi/L	0.1× under
366	Cypress	0.3 pCi/L	0.1× under
367	Opal Cliffs	0.3 pCi/L	0.1× under
368	Broadmoor	0.3 pCi/L	0.1× under
369	Lompoc	0.3 pCi/L	0.1× under
370	Newport Beach	0.3 pCi/L	0.1× under
371	Bonita	0.3 pCi/L	0.1× under
372	Seal Beach	0.2 pCi/L	0.1× under
373	Foster City	0.2 pCi/L	0.1× under
374	Santa Fe Springs	0.2 pCi/L	0.1× under
375	San Lorenzo	0.2 pCi/L	0.1× under
376	Norwalk	0.1 pCi/L	0.0× under

See USA cities ranked by radon level See all States ranked by radon level