it's actually thamnophis elegans vagrans in colorado...some states don't have the most current names or use general names..... Utah listed the valley garters as common garters, thamnophis sirtalis, not t s fitchi....listed the wandering garters as terrestrial garters. I have seen a number of pics of the garters in colorado and they are wandering garters.

for a long while, western terrestrial garters were t elegans terrestris, also known as coast garters. recent studies (I haven't been able to find them yet, but word has gotten around) have removed terrestris and said its another elegans subspecies..not sure if its t e vagrans or t e elegans.