Co-masonic simply means that it is men and women permitted to join.
Freemasonry in the strictest sense is available to males only in the USA.
As far as your approach, you may contact the Grand Lodge in California first (in the USA, Grand Lodges oversee the lodges in their jurisdiction - 1 per state + Washingto DC) - they will get someone from a local lodge to contact you.
You can also go to a local lodge, note their meeting times and dates and phone number and contact them directly - many lodges have websites and you can email them.
You will meet with them and get to know each other a bit first, then you may petition the lodge. If you want to check out other local lodges before deciding on the one to petition that is certainly your right, and it is recommended that you make the most educated decision about the lodge you select.
Basically, to become a Mason, all a man needs to do is ask of his own volition - the Mason you approach will take it from there. You have identified the first step.
Site: http://www.freemason.org/
Join: http://www.freemason.org/join_information.php
Lodge Locator: http://web.sa.mapquest.com/freemason/?tempset=search
Best of luck to you, contact me through my profile if you need additional guidance or help getting started - I'll do what I'm able.