The Isla Angel rattlesnake is endemic to the island of Isla Angel de la Guarda in the Gulf of California. It was previously considered a subspecies of the speckled rattlesnake (Crotalus mitchelli), but was elevated to full species status in 2015. Younger individuals are pinkish-cinnamon colored with brown dorsal blotches and dark speckles intermixed; their color becomes more brown or gray as they age. This species exhibits gigantism, growing to sizes larger than sister species found on other islands or the mainland.

Habitat includes rocky areas such as arroyos (dry gulleys), rocky outcrops, talus and shorelines on the 47 mile long island. They can be found in the lower areas of the island, up to 500m. The Angel de la Guarda Island speckled rattlesnake is a generalist and has been recorded consuming birds, mammals, and lizards. Although there aren't any mammalian predators on the island, kingsnakes are present, and they have been recorded consuming this rattlesnake species.

It is listed as Least Concern by the IUCN, and its population is believed to be thriving due to a lack of human-induced threats, and its range being (naturally) encompassed on a protected island.