Red-Sided/New Mexico Garter snakes

[norcalj]

Other than range, could someone here please tell me what's the difference between the two subspecies (Dorsalis & Parietalis)? Is it scale count? There are individuals from both that look practically identical.

[Stefan-A]

Morphology and presumably reproductive isolation. If they get around to genetic testing, we may know for sure if there is a difference.