Hi, Reed, You may have very possibly found a sharp- tailed snake. I will tell you from experience though, that they can be very difficult to care for. They eat only slugs and slender salamanders, and in my experience, they only seem to eat slender salamanders. They like it cool and moist, and do not get very big at all. I have tried treefrogs, worms, fish- you name it- and only had success with slender salamanders. Slugs are nasty to work with too.
If you know that you can find a steady, nearly year round supply of slender salamanders
B. attenuatus - California Slender Salamander , then you might attempt it, but otherwise I would advise taking some nice pictures of it and releasing it. It probably is brumating, although they can be active in far cooler temps than other snakes.
I have kept a large variety of west coast native snakes, and they have been one the the toughtest for me. I do not currently keep them, or plan to.
Heres one I used to have
Hope this helps.