The California red-sided garter snake (Thamnophis sirtalis infernalis) is a subspecies of the common garter snake. This slender species of natricine snake is indigenous to North America and is one of three recognized subspecies of Thamnophis sirtalis found in California. While commonly confused with Thamnophis sirtalis the subspecies Thamnophis sirtalisinfernalis is biologically part of the population of T. s. tetrataenia, as pointed out by Boundy