Tenants are on a 6 month lease, at the end of 6 months is it automatically a month to month lease in California

Unless the lease specifies an automatic renewal of 6 months

CA lease laws
California Tenants - California Department of Consumer Affairs (http://www.dca.ca.gov/publications/landlordbook/before-rent.shtml)

I didn't see a clear answer on here. From what I remember, the original six month lease was supposed to have a term already in writing as to what was to happen after the lease expired.

As a landlord, you can put the terms any direction that you want, if you give enough notice as stated in the CA laws above.