So, it's been bothering me for a while now. Apparently the taxonomy of Thamnophis elegans has changed a bit and now only two subspecies remain recognized; T. elegans elegans and T. elegans vagrans.

According to:
CNAH
Taxonomic Comments:
  • Hammerson (1999 Amphibians and Reptiles in Colorado. Second Edition. University Press of Colorado, Niwot. xxvi + 484 pp.) presented substantial evidence that the race, Thamnophis elegans arizonae Tanner & Lowe 1989, did not deserve recognition.
  • Hammerson (1999 Amphibians and Reptiles in Colorado. Second Edition. University Press of Colorado, Niwot. xxvi + 484 pp.) presented substantial evidence that the race, Thamnophis elegans vascotanneri Tanner & Lowe 1989, did not deserve recognition.
  • Bronikowski and Arnold (2001 Copeia 2001(2): 508-513), using DNA data, concluded that recognition of the race, Thamnophis elegans terrestris Fox 1951, was unsupported.
So what subspecies do the respective populations belong to now? I'm especially interested in what happened to T. elegans terrestris.