Question: I was legally married in Mexico but have been separated for the last 10 years. Do I need to get divorce in Mexico first before I marry someone in CA?
No! It does not matter what state or country you were arrived in. If you were married anywhere in the world, you must obtain a divorce before you can marry another person. The new marriage would not be valid. It does not matter how long how long you have been separated, you cannot marry someone else until the first marriage is dissolved. Doing so would be bigamy and it is a crime.