In 2019, EAC embarked on an ambitious project to pull together information on Marin County’s groundwater and water resiliency. The report, Beneath the Surface: Groundwater, A Proactive Analysis Exploring California and Marin County Water Resilience in a Changing Climate, was finalized in March 2021.

The report is the first of its kind for Marin County, and we hope to initiate a dialogue on groundwater within the context of water resiliency, which is unfortunately often overlooked in climate readiness forums.

The report seeks to understand groundwater management and regulation in Marin County through a review of relevant background research including local and statewide regulatory frameworks and interviews with key agency staff and experts.

The report also provides an overview of the state and local regulations around groundwater use and basins in Marin County, as well as local climate change-related vulnerabilities.

Download Appendices below (local geological maps provided by the United States Geological Survey):

• Appendix A: Geologic Map and Map Database of Parts of Marin, San Francisco, Alameda, Contra Costa, and Sonoma Counties, California

• Appendix B: Geology of the Point Reyes National Seashore and Vicinity, 1973 

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conserving water

WHERE DO I GET MY WATER?

Check out the below map to view the local water districts in Marin County. If you live outside of one of these areas, then you probably are dependent on spring or well water.

Marin Water
North Marin
Inverness
Bolinas

What is spring water?

Although spring water originates beneath the earth’s surface, pursuant to the California Water, spring water is not considered groundwater. The U.S. Geological Survey defines a spring as:

“…a water resource formed when the side of a hill, a valley bottom or other excavation intersects a flowing body of groundwater at or below the local water table, below which the subsurface material is saturated with water. A spring is the result of an aquifer being filled to the point that the water overflows onto the land surface.”

WHAT IS GROUNDWATER?

Groundwater is water that fills the open spaces between rocks and sediment beneath the surface. Since rocks are generally porous, “groundwater can be found underlying nearly any location” in California.

The best sources of groundwater consist of coarse sediment and are called aquifers. However, groundwater also exists outside of traditional basins and aquifers.

What is a groundwater basin?

According to the California Code of Regulations, groundwater basins consist of aquifers, or bodies of “porous and permeable sediment or sedimentary rock that … yield significant quantities of groundwater to wells and springs” within “reasonably well-defined boundaries.”

Groundwater basins are particularly important because of their water storage capabilities.