[GarterGuy]

Looks like T.r.radix to me. No T.s.sirtalis has the dark spots below the side stripe like your snakes have. That's a very good sign that you've got Plains garters Thamnophis radix radix. Also it looks like the side stripe is up higher on the body.....T.radix has the side stripe on the 3-4th scale, while T.sirtalis has it at the 2-3rd scale. Something else you can check are the number of scales......T.radix has 21 while T.sirtalis has 19. For my money, from the pics you've got up.......I'd say T.radix and considering the area they came from I'd say T.r.radix and not T.r.haydeni (which some people don't even consider a real subspecies anyways).