Page 2 - sarahbrewer_ch1geology

One of the most commonly photographed views of the “Main Rock” looking toward the northwest. Note the severity
of the angles of the varying layers, which include sandstone of different colors and hardnesses. For references in
the following pictures in the report, the Main Rock, as do most of the rocks in the formation, point toward the
northeast. Photograph by Sarah Brewer, 2012.

As these layers were deposited during separate periods by different events, they have created a
physical record of the weather and atmosphere during the periods in which they were created. For
example, much the way tree-ring dating allows us to see years that had a lot of precipitation, or years
that were dryer, these layers in the sandstone can be read to figure out the relative age of events. Because
the layers are made of inorganic materials, they cannot be dated using technology such as radiocarbon
dating, but we are able to see which events happened before or after others, allowing us to construct a
timeline for how the layers were formed. Dry, stable periods made for relatively uneventful (or
nonexistent) layers in the sandstone, while extremely dramatic years, such as those with heavy floods
or landslides, resulted in the opposite: thicker, more complex and dynamic layers, which can contain
various other minerals or even larger pieces of existing rocks. These layers that contain other rocks
(which range in size from small pebble to large boulders) can be seen throughout the park. The
combinations of these different textures and colors result in the fascinating layer-cake look to the
formations in the park.

Aside from this area where massive sandstone slabs were formed, the Vasquez Rocks area is also
located in an extremely geologically active area in terms of earthquake activity. The famous San Andreas
fault, which divides the massive North American and Pacific tectonic plates runs through the towns of
Acton and Palmdale, only miles from the Vasquez Rocks area. An offshoot of the San Andreas, known as
the Elkhorn Fault, actually runs right through the park and has resulted in a large amount of movement
over millions of years.
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