Ventral scales are heavily pigmented, often forming an irregular black stripe.

[2] While it is now considered a valid species,[3] some authorities have classified this snake as a subspecies of the narrow-headed garter snake under the name Thamnophis rufipunctatus nigronuchalis.

[4] The specific name nigronuchalis references the Latin word nigro meaning black, and nuchal meaning of the nape, and is derived from the black neck patch characteristic of the species.

[2] This snake is endemic to Durango state in Mexico,[5] where it is found in wet meadows and riparian areas at altitudes of 8500–9000 feet.

[2] It appears to be restricted to high elevation drainage basins of the Sierra Madre Occidental.