I hiked this Mtn last October and was able to conquer Twin peak and eagle peak but had to turn around because my hiking buddy was out of shape and I didnt want to leave him. So I attempted it again and was able to summit Mt Diablo on Thanksgiving day. It was a beautiful hike. I didnt know it snowed up there so it was a winter wonderland surprise….I met Bruce from the visitor center. Very nice guy, I didnt know it was open. It was also extremely foggy. I started 730 am. It was 27 degrees but I had 3 layers so the cold was no problem. A lot of mountain bikers. I saw a family of deer, birds and rabbits in the white covered mountain. It was a phenomenal experience ♡♡♡