Description: This snake grows to a maximum length of 29+1/2 inches. The smallest gravid female measured was 20+1/2 inches. The color pattern of this species consists of a pinkish, pale brown, yellow-brown, straw-colored, reddish, or yellow-brown ground color, overlaid with a series of brown elliptical or rectangular dorsal blotches. However, most specimens are gray or silvery. In juveniles, the pattern is distinct, but becomes faded in adults, almost to the point where it is indistinguishable from the ground color.

Habitat: C. concolor habitat consists of high, cold desert dominated by sagebrush (Astemesia spp.) and with an abundance of rocky outcrops and exposed canyon walls. Greasewood (Sarcobatus vermiculatus), juniper (Juniperus scopulorum), and other woody plants occur secondarily, or occasionally as co-dominants or even dominants, in some areas. Juniper woodlands are more common at higher altitudes. In Colorado, this species will occupy virtually every terrestrial habitat type that exists within its geographic and elevational range. This includes semi-desert shrubland, riparian zones, piñon-juniper woodlands, and montane woodlands.

Range: Found in the United States in the Colorado and Green River basins. This area covers southwestern Wyoming, Utah east of long. 111° West (excluding the southeastern corner) and extreme west-central Colorado. The type locality given is "King's Ranch, Garfield Co., at the base of the Henry Mts.

Found in these States: CO | UT | WY

Venom: This species possesses the most toxic venom of the C. oreganus / C. viridis group, although apparently considerable variability exists among local populations. It is even one of the most potent venoms found in North America, and according to LD50 studies, the venom is many times more potent than that of an Asiatic cobra. It is characterized by the presence of a presynaptic neurotoxin, referred to as concolor toxin, the amount of which varies in individual snakes.

Diet: Midget faded rattlesnakes feed primarily on cold blooded prey, especially lizards, in part explaining the cocktail of neurotoxins that make up its venom. Rattlesnakes that feed primarily on warm blooded prey typically have venom dominated by haemotoxins, which act upon red blood cells and the circulatory system.

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: