and its just as scared of you as you are of it. call one of those animal control people. truthfully, a garter snake wont hurt you, maybe it was chasing a mouse.. awww, no excuses its gotta go!! so see if you can get that animal control there.
I am not going to get close enough to find out if a snake is poisoneous or not. a reminder though, if its head is diamond shaped, stay away from it!