I can highly recommend Little Basin State Park. http://www.littlebasin.org It is a narrow paved drive up into the hills for a 1/2 mile on a 1 lane road (go in the daytime, you don't want to meet a car at night and have to back up). We had a great time between Christmas and New Year. There is one site with hook-ups called Derksen Grove. This site is out in the open and can be pretty windy at night. All other sites are near water with no hook-ups, but are set up under the canopy of the redwoods. 30s and 40s over night and 40s into the 60s during the day (Late December). Great hiking trails and a beautiful park to see. It was in a little disrepair, but we did go in the winter. We also spent time at Roaring Camp Railroad. https://www.roaringcamp.com I definitely recommend taking the narrow gauge train up Bear Mountain. Great trip for anyone that likes a guided tour through history with the added fun of riding a 115 year old steam train through old-growth redwoods.