National Groups/Organizations

URISA International – Urban and Regional Information Systems Association
GITA – Geospatial Information and Technology Association
AAG – Association of American Geographers
ASPRS – American Society for Photogrammetry and Remote Sensing – see info on Certified Photogrammetrist
ACSM – American Congress of Surveying and Mapping

California URISA Chapters

Northern California Chapter of URISA
Central California Chapter to URISA
BayGeo (BAAMA) Chapter of URISA

Other Southern California Organizations

CGIA – California Geographic Information Association
California GIS Council – Enabling the California geospatial community
Southern California Government GIS Users Group
CalGIS – Annual California GIS Conference
National Geospatial Technology Center for Excellence 

LinkedIn GIS User Groups

GIS, Mapping, and Geo Technology Professionals
GIS and Geography
GIS Professional & Networking

Other GIS User Groups

Geospatial San Diego
San Diego Regional GIS Council – Public Agency GIS Users Group
Orange County GIS Users Group
Inland Empire GIS Users Group – Serving San Bernardino, Riverside, and East LA Counties
Coachella Valley GIS Users Group
Santa Barbara/Ventura GIS Users Group
SoCal Marine GIS Users Group