What is groundwater? Where does it occur in California? What is an aquifer? What is overdraft? … Those questions are illustrated on the Foundation’s beautiful California Groundwater Map poster, which was updated and re-designed earlier this year. Accompanying the map is the easy-to-understand 28-page Layperson’s Guide to Groundwater. … Both products retail for $15 each, but are now available in a bundle during August for $20, plus tax and shipping.