California Geologic History Simplified and related to the Monterey Bay and Canyon Formation Part 1

Introduction The earth is very old – 4.5 billion years old Most of California of relatively new The mountains are still changing, and most features are very young (geologically)—only a few million years old.

The earth’s solid surface (crust) is active and broken into pieces called plates, which slide slowly over the soft layer (Asthenosphere)

Plates Current plates and boundaries Volcanoes occur mostly where one plate is going under another – subduction zones – especially the ring of fire around the pacific ocean. Places where the plates are separating include the mid Atlantic ridge

Types of Plate Boundary Point out the details in the subduction areas with volcanoes above the descending plate as this created much of Ca And the oceanic spreading ridge which created seamounts like the Davidson

Ca Geology Extremely complex Only a few fragments of rocks older than 500 million years Students should have a print out of this for each table Point out the Monterey Bay area , the Sierras and the many “slices”

500 million years ago California, Oregon and Washington were still ocean Quickly show this one

3 D illustration of island arc formation

Dinosaur Era 245-65 mya (Mesozoic) The Sierra Nevada Mountains were pushed up (uplifted) by the formation of the granitic rocks underground The ocean plate continues to push under North America adding a series of slices of old sea floor to the land. Show granite sample and have students find the small ones in their boxes

California stages Spend plenty of time on this slide 170 mya - no central valley or coast range 130 mya - central valley is a sea, and coast ranges are starting 40 mya - central valley is dry. Coast ranges bigger and higher Spend plenty of time on this slide Point out the succession of added slices, the gradual growth of the Sierras

Evidence The slices which were pushed onto Ca contained special deep mantle rocks rarely found on land. These are purple on this map Return to this and point out the slices and thin layers of PURPLE rock

By 100 Million years ago the spreading centers off the Ca coast were getting closer to the subduction zone. The spreading centers formed a series of underwater mountains including the Davidson Seamount The spreading zones are where arrows are shown in opposite directions. There are several not too far off shore. The Davidson seamount is part of the Marine sanctuary. Do cut and paste activity before proceeding to part 2