Description: Adults 15 to 36 inches long, sometimes up to 48 inches with 60 inches being the longest. Neonates are about 10.5 inches in length. Appearance: A heavy-bodied pit viper, with a thin neck, a large triangular head, and a rattle on the end of the tail consisting of loose interlocking hollow segments. Pupils are elliptical. Scales are keeled. Rattlesnakes are "pit vipers" which means they have two pits that are used to sense heat when hunting warm-blooded prey - with one pit on each side of the front of the head above the mouth. Color and Pattern: The ground color is variable, matching the environment - olive-green, gray, brown, golden, reddish brown, yellowish, or tan. Dark brown or black blotched markings, usually with dark edges and light borders, mark the back, with corresponding blotches on the sides. Dorsal blotches mark the front 2/3 of the body, change to dark bars on the body and dark and light rings on the tail which are well-defined and of uniform width. The underside is pale, sometimes weakly mottled. Usually has a light stripe extending diagonally from behind the eye to the corner of the mouth.

Young: Young are born with a bright yellow tail with no rattle - just a single button which does not make a sound. They grow rattles and lose the yellow color as they age. The pattern is brighter on juveniles than on adults.

Habitat: This snake occupies a wide diversity of habitats, from shrubby coastal dunes to timberline, from shrubby basins, chaparral and canyons to open mountain forests. It avoids very arid areas. It is primarily terrestrial but sometimes climbs into trees or shrubs. When inactive, it occupies mammal burrows, crevices, caves, or similar secluded sites. Pregnant females may congregate near the winter den until parturition

Range: In the United States, it occurs in Washington, Oregon, California, western and southern Idaho, & Nevada.

Found in these States: CA | ID | NV | OR | WA

Venom: Rattlesnake bites can cause major, even fatal envenoming. All cases require urgent assessment and management. For larger species, about 20% will have an ineffective bite, with no local or systemic envenoming, so will not require antivenom and may not require prolonged observation. This figure will be higher for the smaller species, which are generally unlikely to cause a severe bite. All other cases, with any degree of local or systemic effects, require extended observation and may require IV antivenom (Crofab), the amount partly dictated by the severity grading. Beware fluid shifts causing shock, coagulopathy and bleeding, kidney damage and necrosis of the bitten area. Some subspecies have caused fatalities (Crotalus oreganus helleri).

Diet: Using its heat-sensing facial pits to locate prey, C. oreganus eats birds, bird eggs, and small mammals, from mice to rabbits. It also eats small reptiles and amphibians. The juveniles eat insects.

Reproduction: Males reach sexual maturity in two to four years, with most reproducing for the first time in their third year. Females in contrast mature in three to seven years, with most first reproducing in their fourth year, however northern populations in British Columbia are known to first reproduce as late as their sixth, seventh, or eighth year. The reproductive cycle of females is normally biennial, although 10% may produce litters in two consecutive years, and one case of a three year interval has been reported. Crotalus oreganus typically mate in the spring after emerging from winter dormancy, although British Columbia populations have been reported to mate in the fall before dormancy. The gestation period was reported to be about 90 days in wild snakes from Idaho, but periods of 143 and 425 days have been reported for individuals in captivity. Females usually fast while they are gravid. They are viviparous, producing live young. Parturition of 1 to 15 (average 3 to 8) young usually occurs in August or September, with neonates ranging 19 to 28 cm. (average 25.2 cm.) in total length. One report of 25 young is regarded as questionable by some herpetologist. Mating usually takes place in concealed areas, like burrows, crevices of rocks and logs, or dense brush. Mating snakes are highly sensitive to disturbance and are quick to separate.

Status: Listed as Least Concern in view of its wide distribution, tolerance of a broad range of habitats, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

Taxonomy: