Western rattlesnake (Crotalus oreganus)
The western rattlesnake is a venomous pit viper in the family Viperidae. GBIF holds 7,526 licensed U.S. records of it; it reaches our listing threshold in 9 states, most of all California (5,224), Washington (859) and Nevada (461). Its observation records peak in May.
Crotalus oreganus, commonly known as the Western rattlesnake or northern Pacific rattlesnake, is a venomous pit viper species found in western North America from the Baja California Peninsula to the southern interior of British Columbia.
From Wikipedia: Crotalus oreganus, text under CC BY-SA 4.0.
Is the western rattlesnake poisonous or venomous?
Yes. The western rattlesnake is a pit viper (family Viperidae), like every rattlesnake, copperhead and cottonmouth in the U.S. Its bite needs emergency care: call 911 and keep the bitten limb still. Antivenom is given in hospital.
Snakes often mistaken for it
Species commonly confused with rattlesnakes and recorded in the same states: gopher snake (recorded in all 9 of its states), plains hog-nosed snake (recorded in 3 of its 9 states) and Great Plains rat snake (recorded in 2 of its 9 states).
Which states have the western rattlesnake?
The western rattlesnake's U.S. record is concentrated: California alone holds 69% of licensed records. It is listed in 9 states in all; the next are Washington (859), Nevada (461) and Utah (427).
The count includes 3 records filed under the older name Crotalus concolor in Utah (2) and Wyoming (1), 2 records filed under the older name Crotalus helleri in California, 1 record filed under the older name Crotalus lutosus in Arizona and 518 records filed under the older name Crotalus viridis in California (202), Nevada (115), Oregon (78) and Washington (123). Records filed under this name in New Mexico are not counted: there the name stands for another species, or the record lies outside this species’ range.
| # | State | Records | Share of state snakes | Rank in state |
|---|---|---|---|---|
| 1 | California | 5,224 | 7.1% | 4th of 46 |
| 2 | Washington | 859 | 16.2% | 3rd of 11 |
| 3 | Nevada | 461 | 11.4% | 3rd of 27 |
| 4 | Utah | 427 | 12.8% | 3rd of 28 |
| 5 | Idaho | 195 | 13.2% | 3rd of 11 |
| 6 | Oregon | 171 | 2.3% | 8th of 16 |
| 7 | Arizona | 119 | 0.6% | 36th of 60 |
| 8 | Colorado | 47 | 1.3% | 8th of 26 |
| 9 | Wyoming | 21 | 2.0% | 7th of 11 |
When is the western rattlesnake seen?
Across the U.S., observation records of the western rattlesnake run mostly March through September, peaking in May with 20% of them. Winter (December to February) holds 2% of them.
Season by state
Among states whose main season falls within one calendar year, it starts earliest in March (California) and latest in May (Nevada, Oregon and Utah). The most common peak month is May, shared by California, Utah and Washington.
| State | Main season | Peak month | Observation records |
|---|---|---|---|
| California | March through September | May | 2,103 |
| Utah | May through September | May | 147 |
| Washington | April through August | May | 54 |
| Oregon | May through August | July | 46 |
| Idaho | April through August | July | 40 |
| Nevada | May through October | June | 39 |
Where the western rattlesnake is recorded in each state
California
California holds 5,224 licensed records, the 4th most recorded of 46 snakes listed there. Its observation records in California run mostly March through September, peaking in May; most licensed records come from San Diego County, Los Angeles County and Santa Clara County. Next come Alameda County (218) and Contra Costa County (192).
Washington
Washington holds 859 licensed records, the 3rd most recorded of 11 snakes listed there. Its observation records in Washington run mostly April through August, peaking in May; most licensed records come from Okanogan County, Kittitas County and Chelan County. Next come Klickitat County (25) and Grant County (22).
Nevada
Nevada holds 461 licensed records, the 3rd most recorded of 27 snakes listed there. Its observation records in Nevada run mostly May through October, peaking in June; most licensed records come from Washoe County, White Pine County and Nye County. Next come Lincoln County (23) and Humboldt County (20).
Utah
Utah holds 427 licensed records, the 3rd most recorded of 28 snakes listed there. Its observation records in Utah run mostly May through September, peaking in May; most licensed records come from Washington County, San Juan County and Salt Lake County. Next come Millard County (38) and Kane County (26).
Idaho
Idaho holds 195 licensed records, the 3rd most recorded of 11 snakes listed there. Its observation records in Idaho run mostly April through August, peaking in July; most licensed records come from Ada County, Adams County and Elmore County. Next come Bannock County (14) and Idaho County (13).
Oregon
Oregon holds 171 licensed records, the 8th most recorded of 16 snakes listed there. Its observation records in Oregon run mostly May through August, peaking in July; most licensed records come from Harney County, Malheur County and Crook County. Next come Jackson County (10) and Lake County (10).
Arizona
Arizona holds 119 licensed records, the joint 36th most recorded of 60 snakes listed there. Most of its licensed records in Arizona come from Coconino County, Mohave County and Apache County. Next come Graham County (6) and Navajo County (5).
Colorado
Colorado holds 47 licensed records, the 8th most recorded of 26 snakes listed there. Most of its licensed records in Colorado come from Rio Blanco County, Moffat County and Mesa County. Next come Montezuma County (3) and Archuleta County (3).
Top counties in the U.S.
| # | County | State | Records | Share of U.S. |
|---|---|---|---|---|
| 1 | San Diego County | California | 1,368 | 18.2% |
| 2 | Okanogan County | Washington | 673 | 8.9% |
| 3 | Los Angeles County | California | 467 | 6.2% |
| 4 | Santa Clara County | California | 330 | 4.4% |
| 5 | Washoe County | Nevada | 222 | 2.9% |
| 6 | Alameda County | California | 218 | 2.9% |
| 7 | Contra Costa County | California | 192 | 2.6% |
| 8 | Santa Barbara County | California | 183 | 2.4% |
| 9 | San Joaquin County | California | 177 | 2.4% |
| 10 | Kern County | California | 173 | 2.3% |
| 11 | San Luis Obispo County | California | 172 | 2.3% |
| 12 | Riverside County | California | 168 | 2.2% |
| 13 | San Bernardino County | California | 130 | 1.7% |
| 14 | Sonoma County | California | 117 | 1.6% |
| 15 | Fresno County | California | 105 | 1.4% |
How recent are the western rattlesnake records?
The western rattlesnake record leans on older material: only 31% of dated U.S. records come from 2017–2026, and the median record is from 1968. The oldest dated record is from 1860; the busiest year was 2024, with 373 records.
| Decade | Records | Share |
|---|---|---|
| 1860s | 3 | 0.0% |
| 1870s | 9 | 0.1% |
| 1880s | 5 | 0.1% |
| 1890s | 46 | 0.6% |
| 1900s | 70 | 1.0% |
| 1910s | 174 | 2.4% |
| 1920s | 398 | 5.4% |
| 1930s | 1,562 | 21.3% |
| 1940s | 591 | 8.1% |
| 1950s | 464 | 6.3% |
| 1960s | 365 | 5.0% |
| 1970s | 232 | 3.2% |
| 1980s | 396 | 5.4% |
| 1990s | 133 | 1.8% |
| 2000s | 271 | 3.7% |
| 2010s | 721 | 9.8% |
| 2020s | 1,890 | 25.8% |
Species recorded in the same counties
Of the 142 counties where the western rattlesnake is most recorded, 122 are also top counties for the gopher snake, more than for any other snake. None of its closest neighbors is venomous.
| Species | Shared counties |
|---|---|
| Gopher snake | 122 |
| Western terrestrial garter snake | 73 |
| Eastern racer | 72 |
| Northern rubber boa | 49 |
| Striped whipsnake | 49 |
| California kingsnake | 48 |
| Coachwhip | 30 |
| Common garter snake | 30 |
Related species in the U.S.
Other species of the genus Crotalus with profiles here: Western diamondback rattlesnake, Prairie rattlesnake, Sidewinder, Timber rattlesnake, Mohave rattlesnake, Red diamond rattlesnake, Black-tailed rattlesnake and Eastern diamondback rattlesnake.
GBIF records read 2026-09-29. Listed: any license. Counted: CC0/CC BY only. How we count.