Thamnophis elegans

Western terrestrial gartersnakes have pale (but not white) stripes on the sides of their body on the second and third scale rows above the edges of their belly scales. They have a bright stripe down their back that extends the length of  their body in some areas, but is dull and fades at midbody in other areas. They often have two large, blackish marks on their neck and irregular black marks on their belly. They have keeled (not smooth) scales. They usually have eight scales on their upper lip on each side of their head. They can reach a total length of up to 42.9 inches (109 cm), but in most areas few exceed 29.9 inches (76 cm).
 

The range extends from central British Columbia, central Alberta, and southwestern Manitoba southward through all of the western United States (east to western South Dakota, western Nebraska, Colorado, extreme western Oklahoma, and New Mexico) to (disjunctively) northern Baja California, with many isolated populations around the margins of the main range. The elevational range extends from sea level to 11,000 feet (3,355 meters), or higher in some locations.

Western terrestrial garter snakes occur in a wide variety of habitats, from lowlands to high mountains, including grasslands, shrublands, woodlands, and open areas in forests. They live on land in most areas, but also in water in some locations like the high Sierra Nevada Mountains. Often they live in wetlands and areas near streams, ponds, and lakes.

Gartersnakes are inactive during cold winter weather. In most areas, they are active from March or April through October or November. They court and mate primarily in spring, soon after they emerge from hibernation. In the mountains, newborns usually first appear in August and early September. At lower elevations, births sometimes occur as early as mid-July.