With the exception of certain public officials, all able-bodied men and women over the age of 18 and not currently serving in the regular armed forces, and any former member of the regular armed forces, are by law already members of the "unorganized" militia. See this article that explains the concept
Laws requiring militia participation are no longer enforced.
Membership in the militia is open to all citizens regardless of race, sex, religion or political affiliation.
Units not open to public membership and/or which are organized for any purpose other than the support of Constitutional principals may be considered private armies and are not to be confused with the Constitutional "unorganized" militia.
As a practical matter, we allow only citizens of good character in the militia.
Those who advocate criminal activity, terrorism, revolution, or a change from our republican form of government are not tolerated or accepted in our organization.
This implies that militia members should understand the duties and obligations of both citizens and government under our Constitution.
Joining the California State Militia is entirely voluntary and as such our members have the right to resign at any time.