Easy. Find the facility there and have him served. If you prep the summary dissolution by yourself and with the help of the family law clinic, 50 bucks max, assuming a waiver on filing fees.
You can contact the facility where your spouse is incarcerated and inquire what their procedure and fees, if any, are for serving someone in their facility. Assuming they have one, you just follow their procedure and they will serve the papers for you. As an example, here is a link to the procedure for a couple facilities in Santa Clara: http://www.scscourt.org/documents/shflyers/INFO%20-%20Serve%20someone%20in%20custody%20w%20map.pdf. Other options may be seeing if your spouse will sign a Notice and Acknowledgement of Receipt to accept service of the papers, or to hire a process server to serve your spouse during visiting hours.
You could file for the divorce in CA in the county that you live in if you have been a resident of the state for 6 months and a resident of the county for 3 months. In order to serve him call the facility in which he is incarcerated and ask for their procedure. Follow their steps and await his response. If he does not serve you with his response within 30 days after you served him then you can Request to Enter into Default and proceed with the divorce without him. Best of luck!
The information you obtain in my answer does not, nor is it intended to, create an attorney-client relationship. You should consult an experience attorney who has knowledge of all the particular facts of your case before making any final decisions.
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