Perhaps nowhere on Earth is such a landscape more dramatically displayed than along the San Andreas Fault in western California. Virgin Islands National Park in the U. Virgin Islands is located on another transform plate boundary, where the Caribbean Plate is sliding past the oceanic part of the North American Plate.
Point Reyes National Seashore, California. Tomales Bay is the surface expression of the San Andreas Fault, seen in the photo below. The granite rocks in the foreground are similar to those found in Yosemite National Park in the Sierra Nevada Mountains. They have been transported about miles kilometers in a north-northwestward direction along the transform plate boundary.
The sedimentary and metamorphic rocks across the fault line are similar to those found in Redwood National and State Parks on the North Coast of California. They were lifted out of the ocean as part of the accretionary wedge of an ancient subduction zone. Left image Tomales Bay. Credit: Photo Courtesy of Robert J. Right image Feature labels. Click on arrows and slide left and right to see labels.
The San Andreas Fault is the transform plate boundary where a thin sliver of western California, as part of the Pacific Plate, slides north-northwestward past the rest of North America. In the Caribbean Sea, the U. Virgin Islands lie along a transform plate boundary where the small Caribbean Plate moves eastward past the oceanic part of the North American Plate. Lillie, New York, W. Norton and Company, pp. This feature includes the famous San Andreas Fault, responsible not only for destructive earthquakes, but also for the spectacular scenery of the San Francisco Bay area and other coastal regions of California.
The San Andreas Fault is responsible for most of the movement in western California, causing a sliver of the state to slide past the rest of the continent. In Mexico, a combinatiion of divergent and transform plate boundary motion is opening the Gulf of California, causing the Baja Peninsula to separate from the rest of Mexico.
Letters in ovals are abbreviations for NPS sites listed above. Marshak, , W. Cabrillo National Monument south of San Diego also lies within the broad zone of deformation between the two plates. The transform plate boundary between the Pacific and North American Plates in western California formed fairly recently. About million years ago, a large tectonic plate called the Farallon Plate started to subduct beneath the western edge of North America.
This resulted in a line of volcanoes stretching all the way from what is now Alaska to Central America. Beginning about 30 million years ago, so much of the Farallon Plate was consumed by subduction that the Pacific and North American plates were in contact, forming the San Andreas transform plate boundary in western California. Over time, the San Andreas transform plate boundary has grown longer as the Farallon Plate split into two separate plates—the Juan de Fuca Plate on the north, and the Cocos Plate on the south.
Remnants of the ancient volcanic mountain chain remain. In central and southern California, for example, the volcanoes have largely eroded away and massive areas of granite from the cooled magma chambers form portions of the Sierra Nevada Mountains, including Yosemite National Park.
Forty million years ago, a large tectonic plate, known as the Farallon Plate, was between the Pacific and North American plates. A transform plate boundary developed where the Pacific Plate was in contact with the North American Plate and the volcanism ceased in central California. Farther east, the continent began to rift apart in the Basin and Range Province. The Sierra Nevada are the eroded remnants of the volcanic arc developed when the Farallon Plate subducted beneath the continent. The San Andreas Fault is just one of several faults that accommodate the transform motion between the Pacific and North American plates.
The plate boundary is a broad zone of deformation with a width of about 60 miles kilometers. Along much of the boundary, the bulk of the motion occurs along the San Andreas Fault. Other parks in the region, namely Pinnacles, Channel Islands and Joshua Tree national parks, Cabrillo National Monument and Santa Monica Mountains National Recreation Area, reveal evidence of the shearing, rotation, and uplift that occurs within the broad zone of deformation between the two plates.
Deformation along the transform plate boundary in California can be visualized by placing a deck of cards between your hands in a praying position. Imagine that your left hand is the undeformed Pacific Plate, your right hand the intact North American Plate. Notice what happens as you move your left hand away and slide your right hand toward you.
The cards slip along their faces, forming a broad zone of shearing between your unaffected hands. For western California, each slipping card face would be a fault surface. Earth's Internal Structure. Divergent Boundary. Convergent Boundary. Transform Boundary. Tectonic Features Map. Transform Plate Boundary. Plate Tectonics Map. What Is The Moho? The East Africa Rift System. What Causes a Tsunami?
Rocks: Galleries of igneous, sedimentary and metamorphic rock photos with descriptions. The Pacific Ring of Fire is an example of a convergent plate boundary. At convergent plate boundaries, oceanic crust is often forced down into the mantle where it begins to melt. Magma rises into and through the other plate, solidifying into granite, the rock that makes up the continents.
Thus, at convergent boundaries, continental crust is created and oceanic crust is destroyed. Two plates sliding past each other forms a transform plate boundary. One of the most famous transform plate boundaries occurs at the San Andreas fault zone, which extends underwater.
Natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions.
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