Mom died, but still legally married to my father. He is technically the executor but out of the picture! Help!

My mother and father are technically married, but have been separated for over 12 years. He is mostly out of the picture. I have been doing EVERYTHING for my mom and her failing health for all of that time. Now that she passed, my father is "next of kin" and the executor. She did not have a will. How can I become the executor so I can take care of all of the necessary legal paperwork without him? I am in San Diego, CA... thanks!!