Crotalus oreganus is a venomous pit viper species found in North America in the western United States, parts of British Columbia, and northwestern Mexico.

The color pattern of the typical form, C. o. oreganus, has a dark-brown, dark-gray, olive-brown, or sometimes black or pale yellowish ground color overlaid dorsally with a series of large, dark blotches with uneven white edges. These blotches are also wider than the spaces that separate them. Additionally, a lateral series of blotches, usually darker than the dorsal blotches, is clearly visible on all but the darkest specimens.

From the Pacific slope in British Columbia, Canada, south through the United States to San Luis Obispo County and Kern County in California, south-central British Columbia, Washington east of the Cascade Mountains, western Idaho from Coeur d'Alene south to near Council or Weiser, northern and western Oregon (excluding the Cascades), and California west of the Sierra Nevada, on Morro Rock off the coast of San Luis Obispo County.