Welcome to the forum family! Garter snakes are very good pets. They are interactive and wonderful company.
That face looks NW to me. If it is, you have a very rare find there. Is it possible to get some more, very clear, pictures of the face and body. You have 4 species of garters in your state. There are subspecies as well so you have several possibilities.

Santa Cruz Garter(Thamnophis atratus):

Western Terrestrial(Thamnophis elegans):

Northwestern(Thamnophis ordinoides):

Common(Thamnophis sirtalis):