I was married in Mexico never registered our marriage certificate w/ the county I live in California? Am I legally married in California?

1. You don't register a marriage in the us, and yes if this was a legal wedding in Mexico you are still married in California,

Some people will record ( not register) their out of the US marriage certificate so it is on file at the court house for future reference.

So you will have to get a divorce if you don't want to be married now.