Living in California is great for a lot of reasons, but one of them is that there are great taxonomy guides around.
The California Herps website is a fantastic resource you can use to ID and report your find, including information on lizards, snakes, turtles, frogs and salamanders. Here's how to use the site:
Determine if the animal you want to identify is a reptile or amphibian, then determine what type of reptile or amphibian you are attempting to identify - a snake, lizard, turtle, frog, or salamander, using the information and pictures below.
If the animal has hair or feathers or lacks a backbone, then it is not a herp and you should look elsewhere.
If the animal has smooth skin that looks wet, with no scales, then it is an Amphibian.
If the amphibian has four legs and a tail, it is a salamander.
if the amphibian has no tail, it is a frog.
Toads are also amphibians - a type of frog - but their skin does not look wet. It is roughly textured, but there are no scales.
Newts also have rough skin at times. They can be differentiated from lizards by their lack of scales.
If the animal is not a fish and it has scales, then it is a Reptile.
If the reptile has legs, but not a large shell on its back, it is a lizard.
If there are legs and a large shell on the back, it is a turtle.
If it has no legs and no shell, then it's a snake (or a legless lizard.)
After you know the type of reptile or amphibian, click on the group name to view a page with pictures grouped by pattern or appearance or other characteristics. Read the brief descriptions and look for a picture of an animal that resembles yours, but beware that many types look similar. When you find the animal, click on the name to view more pictures, information, and a map showing where the animal occurs in California. The maps are general representations of where various animals occur in the state and they can quickly help you determine if an animal occurs in your area.
More info here.