In Joshua Tree National Park, so you have to pay a park entrance fee.
From this spot you have a great view down to the Salton Sea and the San Andreas Fault which reaches from the Salton Sea in Imperial county to Cape Mendocino in Humboldt county.
The San Andreas Fault is a continental transform fault that extends roughly 810 miles (1,300 km) through California in the United States. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The fault divides into three segments, each with different characteristics, and a different degree of earthquake risk.
The origins of the fault can be traced back to the subduction of a spreading ridge 30 million years ago, although the most significant (Southern) segment only dates back about 5 million years. The fault was first identified in the Northern zone by the UC Berkeley geology professor Andrew Lawson in 1895. After the 1906 San Francisco Earthquake, Lawson discovered that it extended into southern California, and Thomas Dibblee's assertion in 1953 that it ran for hundreds of miles took the scientific establishment by surprise.
The plates are continually moving but where the touch each other, they get stuck. As the rest of the plates moves, the stuck parts deform like compressing a spring so they build up stress in the rocks along the fault. When the rock breaks or slips, the suddenly plates move, causing an earthquake. The entire process is called elastic rebound. As they break and scrape by one another, they produce seismic waves that travel through the ground and shake the surface. We know this shaking as earthquakes. While we think of plates as rigid, they can stretch a little, like pizza crust. That is why we can have an earthquake on the San Andreas Fault in northern California but not on the San Andreas Fault in southern California.
There are many major faults in California that are parallel to the San Andreas Fault, like the Hayward Fault. This results in a curious effect: while the Pacific Plate is moving northwest relative to the North American Plate at an average rate of about 2.5 inches per year (about as fast as your fingernails grow), the average slip rate along the San Andreas Fault is less, about 1.5 inches per year. The difference is being taken up by slip along the other parallel faults. This can be demonstrated by a deck of cards.
People often think of the San Andreas Fault as a line in the ground, and that by hopping across it, they can go from one plate to the other. This is not true. Although the most recent break in the ground that defines the trace of the San Andreas Fault is a narrow line, the actual plate boundary should be viewed as a fault zone. The width of a fault zone can be less than a mile wide (Olema Trough) or many miles across (Salton Trough).
You may walk the short trail on you left to get some more information about the things you could see down there.
Logging requirements:
Send me a note with :
- The text "GC4JMEP - Joshua Tree NP - San Andreas Fault" on the first line
- The number of people in your group.
- Walk up the little walk on the left side, while facing the fault. You will see two information boards.
The answer to the following Question: What are their main topics. (Send the main heading e.g.)
- Describe in your own words why earthquakes may happen at a fault zone
Please Note:
- Your logging of this cache and sending me the email should happen at around the same time.
- Spoiler pictures in logs will be deleted without notice.
- Please do not post your answer in you log.
- Feel free to post a picture with you / your GPSr and the beautiful view, but do not post spoiler pictures.
The following sources were used to generate this cache:
- Wikipedia - San Andreas Fault - http://en.wikipedia.org/wiki/San_Andreas_Fault
- NPS - Joshua Tree NP - http://www.nps.gov/jotr/naturescience/faults.htm
- San Andreas Fault Information - http://www.sanandreasfault.org/Information.html
Placement approved by the
Joshua Tree National Park