When it's 50 degrees, they move slower than 60+ degrees, if that provides any comfort. I emailed the snake expert that I linked to in the C2C guide, and he said in Palm Springs they were most likely red pacific diamondback and not western diamondback. It's near a transition region on the map. The other end of the Coachella Valley has western. Higher up on skyline it's the speckled rattlesnakes. I was at the Mill Creek Ranger Station a couple years ago, and somebody told me San G has aggressive black snakes with big heads. I've never seen them, nor have I heard about them from any other people.
On another note, it's really fun to go snowshoeing on a full moon. Very easy to see.
