Most California red-sided garter snakes have a pattern of blue stripes on a black and red background.

[6] The subspecies features an orange or red head, and can vary significantly in appearance based on the geographical location of the snake.

Boundy and Rossman (1995)[2] pointed out some nomenclature problems with the Pacific Coast populations of Thamnophis sirtalis subspecies.

However, T. s. infernalis was primarily replaced by another subspecies of the common garter snake, the valley garter snake (T. s. fitchi), in southern Monterey, meaning that they are absent from Monterey to Santa Barbara, but present from Santa Barbara to San Diego County.

Endangered Species Act (USESA) of 1967,[8] and listed as declining by the United States Fish and Wildlife Services in 1990.

The sag ponds in the San Andreas Fault rift zone and freshwater coastal marshes are their primary habitat.

The California red-sided garter snake is carnivorous - its diverse diet consists of frogs, newts, larvae, fish, birds, and their eggs, small rodents, reptiles, earthworms, slugs, and leeches.

Thamnophis sirtalis infernalis plays a crucial role in their ecosystem, especially with helping control the population of their prey.