Geology of the San Andreas Fault, North American, and Pacific Plates

Geology of the San Andreas Fault, North American, and Pacific Plates

March 24, 2023
Examine oyster fossils and metamorphic rocks on each side of the San Andreas fault to piece together the geologic story of Point Reyes.

Explore the different geology of the North American and Pacific Plates on opposite sides of the San Andreas Fault at Tomales Bay State Park. The morning hike at low tide examines river gravels of Franciscan rocks (pillow basalts and cherts) and fossil oyster beds exposed in the sediment bluffs on the North American Plate at the Millerton Point unit near Highway 1 north of Point Reyes Station.

The afternoon hike will examine the granitic and metamorphic rocks displaced from southern California on the Pacific Plate at Heart’s Desire and Indian Beaches off the Pierce Point Ranch Road.

State park entrance fee is not included with registration.

John Karachewski has conducted geology and environmental projects from Colorado to Alaska to Midway Island and throughout California. Doris Sloan and John collaborated on a popular book about the “Geology of the San Francisco Bay Region.” John enjoys biking, hiking, and photographing landscapes.

Photo Credit: Robert Campbell


-We will be meeting at the Tomales Bay State Park – Millerton Point parking lot

– Please arrive 10-15 minutes early to check in

– Refunds available for all classes 7 days in advance of the start date, after 7 days and before 2 days, participants can credit their class for a future date. All requests before 48 hours in advance will be declined. For COVID cancellation policy, see below.

– Please follow the parking instructions for the facility used that day

– Please provide an email you check regularly for updates and reminders about your class

– Registration is required online prior to the event in order to maintain class sizes

– Sales end 48 hours before the start date.

– Waitlists are available when the class sells out

What to Bring

Trekking poles if desired (optional)

Day Pack


Warm Variable Weather Clothing

Hiking Shoes

Water Bottle

Notebook and Pen/Field Journal

Eventbrite Confirmation Email

Binoculars (Optional)

Camera (Optional)

About the PRNSA Field Institute

The PRNSA Field Institute offers hands-on environmental education classes throughout the year that foster enjoyment of Point Reyes National Seashore. Our classes are led by expert instructors, who take you out of your everyday life and into the natural world. We host a variety of classes about the arts and sciences and have something for everyone. You can reach the Field Institute at (415) 663-1200 x304 or by email at

Interested in becoming a member of PRNSA? Click Here!

Interested in becoming a PRNSA Field Institute volunteer facilitator, or are you an outdoor educator or artist who would like to teach a PRNSA Field Institute class? Send an Email!

For any questions, please email us at

COVID-19 Field Institute Guidelines

In accordance with Marin County guidelines for public health and safety, we ask all participants to respect the following COVID-19 procedures:

• Perform a health self-check before coming to class using the CDC Symptoms of Coronavirus as a guide

• Do not attend class if you are experiencing COVID symptoms, suspect you have been exposed to the virus, or are suffering from any other flu-like or respiratory illness

• Participants exhibiting signs of respiratory illness may be asked to leave class

• Masks are optional but are strongly recommended when indoors or if gathered closely outside

• Please bring your own food and water

NOTE: Refund policy exceptions will be made for participants cancelling last minute due to COVID-19 infection or symptoms. Please contact us in this case.

Thank you for your cooperation in following these guidelines to help keep everyone safe.