The various subspecies of Crotalus viridis may vary slightly in color. Most are greenish gray or greenish brown in color, although members of one subspecies are black with only slight markings. These rattlesnakes have from 33-55 dark blotches on their back, which flatten into rings on the tail, surrounded by lighter markings. Juviniles have similar markings to adults, but may have higher contrast in coloring. All Crotalus viridis have a rattle at the end of their tail, made up of segments of keratin, which knock together to make a rattling sound. The number of segments varies because each time the snake sheds its skin, it gains another segment. Crotalus viridis is generally about 91.5 cm in length, but can be from 89-114 cm. Males and females are dimorphic in that the number of rings on their tails differs. Males tend to have between 6-15 rings, and females tend to have between 4-11 rings.
There are nine subspecies of Crotalus viridis. Crotalus viridis viridis , or Western or Prairie rattlesnake, is the most widespread and is found in most regions of the species. There are eight others which are mostly named for the region they are found in. They are Grand Canyon rattlesnake (Crotalus viridis abyssus), Coronado Island rattlesnake (Crotalus viridis caliginis), Arizona Black rattlesnake (Crotalus viridis ceberus), Midget Faded rattlesnake (Crotalus viridis concolor), Southern Pacific rattlesnake (Crotalus viridis helleri), Great Basin rattlesnake (Crotalus viridis lutosus), and Hopi rattlesnake (Crotalus viridis oreganus). (LaDuc, 2000; Melli, 1999; Herp-edia, 1998; Reptiles and Amphibians of North Dakota, 1999)