Northern California Geological Society
Exploring Deeply Subducted Rocks on Angel Island
Retired geologist and NCGS President Elect
Don has has 30 years experience in research and technical services in the oil industry, multiple publications in structural analysis and modeling, and is currently NCGS Treasurer.
Bill has 50+ years as a Professional Geologist and 35+ years of experience in environmental, geochemical, and water quality investigations. Bill’s currently a NCGS Councilor, providing support for meetings and field trips.
The Franciscan Complex is one of the best-known ancient subduction complexes in the world and is exposed throughout the northern San Francisco Bay area. Pre-Quaternary rocks on Angel Island are exclusively Franciscan complex, but represent a range of metamorphic grade from unmetamorphosed to blueschist facies representing burial deeper than 25 km.
Lithologies we will observe range from serpentinized ultra mafic rocks, through gabbros and pillow basalts, to chert and greywacke turbidites. Deformation states vary from minimally deformed greywackes to highly sheared ultral mylonite meta mafic rocks representing a subduction mega shear zone.
The material presented will include new research by NCGS scholarship recipient Meg Das, original work by the leaders, and literature review.
We will circulate an attendees list for carpooling to the field trip locations.
Field Trip Reminders:
This trip will begin and end with ferry rides so we will not have access to vehicles during the trip.
Once on the Island, we will begin the trip with an open tram ride from Aylay Cove on the north to Four Corners on the southeast side. From there we will walk approximately 3.5. miles on the paved perimeter road, with two excursions down beach outcrops.
Each beach decent is about 50 m vertical on unmaintained, rough single track trails and beach outcrops will be wet and slippery. Hiking boots and poles are strongly encouraged. Once on the beaches we will walk about 1/2 mile on each. Thus total walking for the day will be about 4.5 miles spread out over 4 or 5 hours.
Restroom facilities are available at the ferry landing and at Kayak Camp which we will pass by at approximately 2 pm and 3:30 pm. Potable water is available at the ferry landing and three locations which we pass during the walk.
THIS FIELD TRIP WILL BE LIMITED TO 22 PEOPLE.
**********************. Field Trip Logistics *******************************
Date: September 28, 2024
Time: The trip will begin at 9:45 am and end at 5:30 pm. We will take the 10 am ferry to Angel Island from Tiburon and plan return to Tiburon on the 5:20 pm ferry. However, if we finish early, there is a chance to take the 4:20 ferry instead.
Meeting Location: Meet at the Angel Island Tiburon Ferry, 21 Main Street, Tiburon, CA 94920
Ferry ticks: Tickets can be purchased on site, but to ensure space and expedite boarding, please by tickets in advance online by clicking on the September 28th date at the following link: https://angelislandferry.com/schedule. Park entrance is included in the ferry fee.
Cost: Fee covers the direct costs of the 40 page field trip guide and the tram ride. Lunches will NOT be provided and services on the Island are limited to the ferry dock, so remember to bring your own!
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