Here are 2 options i came up with:
1. Restrict new members that are located within the 90000 to 93599 Zip Codes of Southern California. Upon new user registration, they are required to enter the zip code. If it does not fall into that range of 90000 to 93599, then they are denied access.
2. A location map for Admin view only of the IP Address of each member. Shows a Map with droppins of each member. If i see an IP Address out of the range, I will deny their registration or remove them from the community.