The Pacific Western Rattlesnake (Crotalus viridis) is a common reptile species found at the UC Hopland Research & Extension Center. Found in almost all habitat types at the Center, this sole rattlesnake species found in Northern California seeks out rocky outcrops, rock boulders, rock rip-rap areas (above water line), and occasionally man-made out-buildings, junk piles, and the like to find safe thermal refuge from the winter rains and low temperatures.
All of these "den" areas require some sort of crevice or cavity that stays dry during the winter. From research on other ratttlesnake species in the eastern U.S., scientists know that rattlesnakes do not instinctively go to a certain winter den site. However, in their first year of life, they do instinctively follow the scent of other rattlesnakes in the fall of the year ...and that usually leads them to a den site. Once they retire in "that" winter den site for their first winter, then they usually will return to the same den site each subsequent year after.
Evidence of shed skins is usually a sign that rattlesnakes either use the area for summer refuge and or winter retire (winter dens).
