Volcanic Activity Risk in California
All California counties ranked by FEMA National Risk Index volcanic activity score
Volcanic Activity risk — eruptions producing ashfall, lava, and pyroclastic hazards — is rated for 46 of 58 California counties in FEMA's National Risk Index. Siskiyou County carries the state's highest volcanic activity score at 98.0, with $2M in expected annual volcanic activity losses.
1 California county is rated High or Very High for volcanic activity, and expected annual losses from volcanic activity total roughly $2M statewide. The full ranking below links to each county's complete 18-hazard risk profile.
County Rankings — Volcanic Activity
| # | County | Volcanic Activity Score | Rating | Ann. Freq. | Ann. Loss |
|---|---|---|---|---|---|
| 1 | Siskiyou County | High | 0.00 / yr | $2M | |
| 2 | Lake County | Medium | 0.00 / yr | $484K | |
| 3 | Shasta County | Medium | 0.00 / yr | $245K | |
| 4 | Tehama County | Low | 0.00 / yr | $58K | |
| 5 | Plumas County | Low | 0.00 / yr | $8K | |
| 6 | Mono County | Low | 0.00 / yr | $12K | |
| 7 | Lassen County | Low | 0.00 / yr | $3K | |
| 8 | Imperial County | Low | 0.00 / yr | $2K | |
| 9 | Sonoma County | Low | 0.00 / yr | $3K | |
| 10 | Modoc County | Very Low | 0.00 / yr | $821 | |
| 11 | San Joaquin County | Very Low | 0.00 / yr | $515 | |
| 12 | Butte County | Very Low | 0.00 / yr | $392 | |
| 13 | Sacramento County | Very Low | 0.00 / yr | $377 | |
| 14 | Alameda County | Very Low | 0.00 / yr | $348 | |
| 15 | Stanislaus County | Very Low | 0.00 / yr | $316 | |
| 16 | Contra Costa County | Very Low | 0.00 / yr | $343 | |
| 17 | Mendocino County | Very Low | 0.00 / yr | $199 | |
| 18 | Tulare County | Very Low | 0.00 / yr | $108 | |
| 19 | Solano County | Very Low | 0.00 / yr | $108 | |
| 20 | Placer County | Very Low | 0.00 / yr | $95 | |
| 21 | Riverside County | Very Low | 0.00 / yr | $72 | |
| 22 | Inyo County | Very Low | 0.00 / yr | $48 | |
| 23 | Marin County | Very Low | 0.00 / yr | $56 | |
| 24 | Madera County | Very Low | 0.00 / yr | $33 | |
| 25 | Yolo County | Very Low | 0.00 / yr | $51 | |
| 26 | Tuolumne County | Very Low | 0.00 / yr | $39 | |
| 27 | El Dorado County | Very Low | 0.00 / yr | $40 | |
| 28 | Napa County | Very Low | 0.00 / yr | $33 | |
| 29 | Kern County | Very Low | 0.00 / yr | $25 | |
| 30 | Calaveras County | Very Low | 0.00 / yr | $24 | |
| 31 | Sutter County | Very Low | 0.00 / yr | $24 | |
| 32 | Mariposa County | Very Low | 0.00 / yr | $17 | |
| 33 | Nevada County | Very Low | 0.00 / yr | $23 | |
| 34 | Yuba County | Very Low | 0.00 / yr | $22 | |
| 35 | Trinity County | Very Low | 0.00 / yr | $14 | |
| 36 | Fresno County | Very Low | 0.00 / yr | $14 | |
| 37 | Glenn County | Very Low | 0.00 / yr | $17 | |
| 38 | Merced County | Very Low | 0.00 / yr | $10 | |
| 39 | Amador County | Very Low | 0.00 / yr | $10 | |
| 40 | Sierra County | Very Low | 0.00 / yr | $8 | |
| 41 | Colusa County | Very Low | 0.00 / yr | $5 | |
| 42 | San Diego County | Very Low | 0.00 / yr | $3 | |
| 43 | San Bernardino County | Very Low | 0.00 / yr | $3 | |
| 44 | San Francisco County | Very Low | 0.00 / yr | $1 | |
| 45 | Alpine County | Very Low | 0.00 / yr | $0 | |
| 46 | Santa Clara County | Very Low | 0.00 / yr | $0 |
46 California counties with measurable volcanic activity risk. See the national volcanic activity ranking or all California counties by overall risk.
Frequently Asked Questions
Which California county has the highest volcanic activity risk?
Siskiyou County has the highest FEMA volcanic activity risk score in California at 98.0 (High), with $2M in expected annual losses and about 0.00 events per year.
How many California counties face significant volcanic activity risk?
46 California counties record measurable volcanic activity risk in FEMA's National Risk Index; 1 of them are rated High or Very High.