What specific characteristic is associated with the nominate subspecies *Crotalus o. oreganus*?

It is frequently associated with the common name Northern Pacific Rattlesnake and covers the northwestern range extent.

The subspecies designation *Crotalus o. oreganus* holds the status of the nominate subspecies, meaning it often serves as the baseline or type specimen reference for the entire species *Crotalus oreganus*. This particular form is strongly linked geographically to the northwestern extent of the species' distribution. It is the form that is frequently recognized and named the Northern Pacific Rattlesnake in areas like British Columbia. Other subspecies, such as *C. o. lutosus* or *C. o. concolor*, are associated with different regional forms found further south or east within the broader species range, depending on the taxonomic schema applied.