Marin Headlands: photograph of Marin Headlands from the Golden Gate Bridge by Christopher BelandSummary
The Marin Headlands contain the geologic record of a great deal of plate tectonic action that can be used to piece together the history of the formation of California. Briefly, around 180 million year ago, the North American plate collided with a now subducted plate called the Farallon plate. As the Farallon plate dove under the North American plate, bits and pieces of the Farallon plate were scraped off. These bits and pieces can be found in the Marin Headlands in several distinctive rock formations: pillow basalts (at the Point Bonita Lighthouse), chert (near Rodeo Lagoon), and sandstone (at Rodeo Beach). By closely observing these rocks and figuring out how they formed, an understanding of how California itself was formed may be inferred.
Note #1: If you are intimidated by the trip as described here and prefer to have park rangers lead your field trip and geology investigations, consider participating in “Rocks on the Move”. This free program provides teacher training, pre- and post-visit curriculum, as well as a very knowledgeable ranger to lead the field trip portion of the visit.
Note #2: The geologic investigations undertaken in this field trip require students to have a good understanding of the rock cycle and the geologic time scale (see Geology Box) as well as exposure to the theory of plate tectonics. It is designed as a culminating field trip to tie lots of ideas together into a cohesive theory.
Can make observations about the types of rock in the Marin Headlands.
Can model convergent, divergent and transform plate boundaries.
Can understand the conditions under which different types of rock form.
Can use evidence from rocks to piece together a theory of how California formed.
Can model the formation of California using sand castles.
North American plate
Law of Original Horizontality
Law of Superposition
Law of Lateral Continuity