cold baby blue belly

Question
I was in the backyard of my San Jose CA home playing with my ball with my pup.  I reached down to pick up a tennis ball when a baby blue belly lizard literally landed in my hand (figured it jumped or fell from the fence) I was surprised at how tame it was, it seemed to enjoy being held and closed his eyes while I was petting him.  I then put him back where I found him and he crawled under a pile of leaves.  The following day, I was out playing with my pup again and found the lizard in the same spot that I left him.  It worried me because it's been getting pretty cold here lately (think it was supposed to be around 30F last night).  I picked him up, and he was so cold he could barely move.  I held him in my hand and brought him inside to warm him up.  It seemed to work because all of a sudden he got very active and jumped out of my hand and the warm lizard was much harder to catch.  I've done some research on caring for blue bellies, and I'm considering keeping him inside for the winter and releasing him when it gets warmer.  It is not my intention to hold the poor little guy hostage and keep him as my pet, but I thought they were supposed to be in hibernation right now and don't want him to freeze and die outside either.  Could you please tell me what you think would be best for him?  Thank you for your help.

Answer
Hi Marisa,
Its best to return him to the place you found him. Do this during the day.  As you have found out, he wasn't calm because he was enjoying being held, it was due to being cold, which is normal. Many lizards actually need to have the "cooling down" of the winter to be able to breed in the spring.
The place where he was (under the leaves) is where he chose to spend the colder night.
He may come out during the day into the bright sunshine to warm up and then go into rocks or under leaves for the night.
You say "baby"...lizards from hatching(or birth) are on their own to survive and they learn very quickly just how to do that.  It's natures way of having the strongest survive.
No reptiles should ever be removed from their natural habitat... I understand and appreciate greatly that you aren't wanting to hold him hostage, but want to help him.  The best way to help him is to place him outside during the day, in the area you found him.  If you want to and feel he needs it, you can make a little cave like area for him with rocks under some leaves so that he can climb into that.  The rocks will warm during the day and keep him from freezing at night.  They are very good with natural instincts.
With the seasons, they basically gradually cool down due to the temperatures. Its natures way.  What they do is sort of like hibernation but, on warm sunny days they will warm up, come out and eat and retreat to their hiding place at night. They are able to go extended periods with no food when its colder and no sun as their body temperature lowers, their metabolism slows which is how they survive the cold temperatures.
If you are lucky, you may see him popping his head out on sunny days and come spring, he can help keep all the nasty insects away...I've heard it said that areas that have the fence lizards have a much lower incidence of Lyme's disease!!