Occurrence of the Garter Snake, Thamnophis sirtalis, in the Great Plains and Rocky Mountains

The common garter snake stretches across most of the United States, from the Atlantic seaboard to the Pacific coast, and reaches far into Canada and even southeastern Alaska. Its many subspecies—each with distinct color patterns and regional ties—make it a living puzzle for herpetologists. Among them, the western forms display striking red markings that set them apart from their eastern cousins, hinting at a complex evolutionary story.

In this detailed study, the authors turn their attention to the parietalis group, aiming to map its western boundaries and untangle its relationships with neighboring subspecies. They revisit historic descriptions, clarify long‑standing confusion over the original type locality, and trace how early taxonomists shuffled names as new specimens emerged. By weaving together field observations, museum records, and a thorough review of past literature, the work offers a clearer picture of how these snakes have spread across the Great Plains and Rocky Mountains, inviting listeners to explore the subtle geography behind a familiar reptile.