Crotalus willardi obscurus is a venomous pitviper subspecies[4] found in northwestern Mexico and the Southwestern United States.

In the Sierra San Luis population, traces of the pale upper facial stripe may be visible on the posterior upper labials, but there is no pale stripe on the lower labials.

[5] The type locality given is "one canyon in the Animas Mountains" (New Mexico, USA).

Fish and Wildlife Service, and is therefore afforded protection by the Endangered Species Act.

It is listed because of its limited geographic range and the supposed threat to it of overcollection for the reptile trade.