Common Names: Black-tailed rattlesnake, green rattler, northern black-tailed rattlesnake, dog-faced rattlesnake, dog-headed rattlesnake, mountain diamondback.
Habitat: Grasslands, desert areas, rocky and mountainous areas, as well as higher altitude forested habitats. Max elevation ~9500 feet. Known to climb and swim. Arizona and New Mexico into west and central Texas, plus northern Mexico and Gulf of California.
Description: 30-42", females being larger. (Largest on record was 50".) Color may be yellow, olive green, brown or black. Distinguishing feature is the tail is always black. (Thus the name. ;-) May have a black band from the corner of the mouth, across the eyes, to the opposite corner of the mouth.
Comments: May move rectilinearly or sidewind, depending on terrain.