The Santa Catalina Island rattlesnake is endemic to Isla Santa Catalina in the Gulf of California. It is an exceptionally slender, medium size rattlesnake. Among rattlesnakes, it is unique in that it lacks a functioning rattle-- the base "button" falls off with every new shed, preventing growth of the rattle.

Small mammals and lizards provide a stable food source for this species. It is also remarkable in that it is the most arboreal of the known rattlesnake species, often using trees and shrubs to hunt. Experts believe that this species arose from red diamond rattlesnakes (Crotalus ruber) which washed ashore on Isla Santa Catalina long ago.

It faces extinction due to illegal poaching and invasive predators (such as feral cats).