Geology 15                                                                                          West Valley College

Geology of California                                                                                  Robert Lopez


Study Questions 15: Coast Ranges and Marine Terraces


1)      What is the age of the Franciscan Formation and what is its tectonic environment.


2)      What are the principle rocks of the Franciscan Formation? Name the marine rocks and the ocean lithosphere rocks.


3)      Much of the Franciscan is a “melange”; what is a melange (plate 4, Fig. 12-16)?



4)      Make a simple three-part sketch (like the one we did in class) showing the development of the San Andreas Transform (also see Harden, Fig. 12-2, p. 282).


5)      What are the plates involved in the Mendocino triple junction?


6)      When was the initial contact between the Pacific Plate (East Pacific Rise) and North American Plate?


7)      Why is the distinction between the San Andreas Transform and San Andreas Fault important?


8)      What is the Salinian Block?



9)      Compare the Salinian Block basement rocks (Mesozoic granites, metamorphic roof pendants) with those of the Franciscan Formation (subduction zone rocks).


10)  What does the Salinian Block represent in terms of plate tectonics, where are its boundaries, where did it originate, and how far has it traveled (read the following notes from lecture)?


The Salinian Block is an area in the Coast Ranges underlain by granitic and high-grade metamorphic rocks that is bound on the east by the San Andreas Fault and on the west by the Sur-Nacimiento Fault zone.  The basement of the Salinian Block, which represents a CONTINENTAL MAGMATIC ARC, contrasts sharply with those of the Franciscan Formation that lies both to the east and west.  (Recall, the Franciscan Formation has oceanic affinities – e.g. contains fragments of oceanic crust and not granites are present.  The rocks of the Franciscan Formation were deposited in a trench at a convergent boundary, subducted, and metamorphosed at HIGH PRESSURE and relative low temperature.)  Rocks of the Salinian Block originated in the area of the present Mojave Desert region, between the southern Sierra Nevada and the Peninsular Ranges batholiths, and they have been displaced at least 315 km (180 mi) northward by movement on the San Andreas Fault.


11)  What kind of rock forms the Pinnacles in the Pinnacles National Monument?


12)  What is the approximate age of the Pinnacles and Neenach volcanic fields, what is their geographic relationship, and what evidence do they provide concerning movement along the San Andreas fault?




Geology and Geography of the Local Coast Ranges


On our field trip, we will see these prominent geographical features: Santa Lucia Range, Salinas Valley, Gabilan Range, Santa Cruz Mountains, and Loma Prieta.


On the cover of your textbook, locate the following: Monterey Bay, Santa Lucia Range, Salinas Valley, Gabilan Range, Santa Cruz Mountains, Ben Lomond Mountain, Santa Clara Valley, and the Diablo Range.


Make sure you read the attached excerpt from Steinbeck’s East of Eden.  Relate Steinbeck’s description to the mountains and valleys visible across Monterey Bay.


Marine Terraces (Harden, p. 415-418)


1)      What are marine terraces?


2)      What two factors interplay to form marine terraces?


3)      How do periods of glacial maxima (glaciers advancing on continents) correspond with sea level changes?


4)      What was the elevation of sea level during the last glacial maximum (?


5)      How high would sea level be if all the present glaciers melted?


6)      Sketch a diagram of the following: modern wave cut platforms; marine terraces; modern and ancient sea cliffs and shoreline angles; terrace deposits.


On plate 29 of your textbook (color plates between page 64-65), be able to identify the Santa Cruz Mudstone, the Santa Cruz Age marine terrace, and the terrace deposits (Harden’s caption is in error in describing the SC mudstone as a sandstone).