Melanistic Southern Pacifics are found typically at higher elevations of the "Angeles Crest" and the San Jacinto Mtns as well i.e; the home to the town of Idlewild. Once you start seeing pine trees you're in dark/black southern territory. Presumably an adaptation to the colder temperatures found therin, imagine the difference a melanistic snake has in attaining a desirable body temperature when exposing some small portion of it's body in a rock crack let alone laying out fully in early spring or late fall sun. Another interesting note is their ability to change color from a grey to dark black and back again. Arizona Black Rattlesnakes also display that trait.... the change may be related to light cycle (day or night) or stresses on the animal, not simply temperature. I have personally seen a cerberus turn from a deep black to a light grey unrecognizable animal complete with classic facial stripes merely after a car ride!