Hopefully others can comment on specifics - but to me that looks like some sort of small woodland plethodontid (a member of the family of lungless salamanders). I would think you should feed it very small fruit flies, very small crickets, possibly calcium dusted (especially since it appears to be young) and I would keep it fairly moist, possibly on paper towel. This is how I would keep the redbacked salamanders I caught.
Take this all with a grain of salt - I do not have any idea of exact species. What you can do is look up a list of salamander species of California, scroll through and see, based on photos, which one matches. Then you can google care from there, and do research on its habitat and niche if captive care information is lacking
