This is a red eared slider. It needs to have a body of water to swim around in. They are only able to eat in water. So if you don't get him into water he will dehydrate and/or starve to death.

They are not native to CA. So this is just a turtle that somebody dumped or that got away from someone.

Don't release it into a pond. Get him set up in a tank or an outdoor goldfish pond or something. Or find him a home. You can go to the Red eared slider forum to get the info. you need on a proper setup for him.

Steve