Although largely aquatic in habits, this species sometimes ventures out onto dry land as seen here. Taxonomy is complex. This snake is currently considered a subspecies of the Aquatic Garter Snake, having been split from the Sierra Garter Snake (T. couchii) in 1987. Prior to that it was treated as a race of Western Terrestrial Garter Snake (T. elegans). This location is near the northern limit of its range, beyond which it intergrades extensively with the Oregon Garter Snake (T. a. hydrophilus). iPhone 5.
Reference:
Nafis, G. (2000-2016) California Herps - A Guide to the Amphibians and Reptiles of California. Available at: http://www.californiaherps.com/ (accessed 30 August 2017)..