Majority of range is in western Mexico, along the Sierra Madre Occidental mountain range, but its northern boundary extends into the southeastern corner of Arizona and southwestern corner of New Mexico.
This secretive species inhabits mountainous woodlands at high elevations. It prefers areas with dense canopy cover and plentiful leaf litter. There are 5 subspecies, each limited to their own mountain ranges.
A somewhat small venomous pit viper, measuring 1-2 feet in length. It has mildly keeled scales, and it's named for the unique upturned scales around the top edge of its snout. Its pattern and coloration is variable, but in general its face is more distinctly patterned than the rest of its body. It has 2 horizontal light lines on each side of the face, separated by dark (usually brown) coloration. The dorsal lines are thicker and run from the tip of the snout to the corner of the jaw. The ventral lines are thinner and begin along the upper lip, then cross the mouth and extend down the lower mandible. When viewed from the front, a thin vertical light line is also present down the center of the snout. The rest of this snake's body is typically a mid-toned background color adorned with thin light dorsal bands that do not extend down its sides. These bands are edged with dark scales. Most individuals have muted dark spots on their sides.
Learn more with Schechter Natural History's Guide to Reptiles and Amphibians