June 15, 1805, Great Falls, Cascade County, Montana.
Usually greenish to brownish (some populations pinkish to reddish-brown) above. Well-defined brown blotches down midline of back; white to yellowish lines on head slanting backward. Length: 0.8-3.8 ft (0.3-1.1 m).
Great Plains grassland to rocky outcrops, talus slopes, and prairie dog towns.
Extreme western Iowa to the Rockies, southern Alberta to northern Mexico.
The prairie rattlesnake, which occupies a large swathe of the central part of North America, used to be considered a subspecies of the western rattlesnake, Crotalus oreganus.