Now that we got that out of the way, lets begin with a basic geology lesson. What is really interesting here is how these mountains came to be. Everyone knows about the San Andreas Fault and how it's famous, but what many people don't realize is that it crosses Interstate 5 a few hundred feet away from here. In fact the fault line crosses the interstate not once, not twice, but three times. This location is the most western point at which the San Andreas Fault line crosses Interstate 5. The other points of intersection are near the northbound exit and southbound onramp at exit 202 and again at Highway 138.
Before I go into any more details lets first discuss the basic fundamentals of how fault lines are created and now they work. The answer can be found in your kitchen, literally. When boiling pasta on the stove, the hotter pasta floats to the surface then when it cools it sinks. This effect has a name. Convection currents in your pot at home and in the earth are nearly identical. There are a few difference though. One is with water, rather than boiling rocks and the other is that one is less a few inches while one is miles deep. Convection currents are continues cycles in the earth's mantel that make hotter rock rise, and cooler rock fall and the cycle begins over and over again. When this happens, it causes fractures in the earth's crust. When fractures occur, a fault line is created.
Now at this point I'm sure you are asking, "What is a fault line?" Well, it is place where two tectonic plates meet and create friction. When this friction is released, an earthquake is formed. This friction is formed by these convection currents. When they move in a circular pattern in one direction, they can push rock with them. When tension is released you get an earthquake in an that moves in waves on the X, Y, and Z axises. X is up or down, Y is right or left, and Z is pivoting side to side.
Depending on the pressure, it can create a magnitude 1 earthquake on the Richter Scale or a 10. A 10 has never happened in recorded history, but is believed to have only occur when large meteors hit the earth. The largest earthquake ever recorded happened in Chile on May 22, 1960. It happened in open waters, just off the coast in the Pacific where it created a Tsunami. You can see my earthcache about that Tsunami
here.
A Richter Scale works like this. Say there was a 5.0 earthquake, which are common, and a 7.0, a little less. A 7.0 on the Richter scale is 100 times greater of that of a 5.0 on the same scale. Each decimal point in-between is twice as as bad as the preceding one.
So how do we predict such event? We can use a number of devices that monitor the fault line or zone, as it is more scientifically correct. The fault zone can be monitored by using lasers or GPS. Both have downsides, but both are extremely precise in measuring the activity. By using lasers, we can accurately measure how far the fault moves in a year, which is the same rate as an average human's finger nails grow. GPS systems are a little bit better in tracking the movement and direction of the fault zone. By using survey disks and benchmarks, we can accurately measure the direction and move rate of the fault zone and predict what it will look like in the future.
GPS Fault Map Movement
**NOTE** - Do you see that there are more than one GPS device? There has to be at least two on either side of the fault so the results of the data can be compared. This is the most accurate way of predicting fault movement. These types of SCIGN GPS stations are permanent and will likely never be moved from the point at which it is set into the ground. At the geocache site, you will not see one of these permanent GPS receivers. Instead, you will see a survey disk where old methods of survey can take place. It is better as it is less expensive, but will not keep continuous data flowing into a server.
So, what is special about this particular earthcache? At this location, you can see two different tectonic plates that the San Andreas Fault creates. To the north of the fault line, this location, you are on the North American Plate which covers most of North America and half of Iceland. To the south of you, is the Pacific plate which covers Los Angeles, Baja California, Hawaii, and parts of Alaska before reaching the Mariana Trench near Japan. Here, you can see the two individual plates by their difference in color. The Pacific plate is on top in white rocks (limestone) and the North American plate in red just below it. The point of intersection between these two rocks is the San Andreas Fault. This is one of those rare opportunities where you can see it up close, rather than on an aerial view.
Limestone is formed from the decay of marine life. When they die, they sink to the bottom. Now, all living things must have phosphorous as it makes up DNA. When the animal dies, the phosphorus decays as well and over time, forms a hard layer of rock we know as limestone. Limestone gets its distinctive color from the calcium in the rock from other parts of decaying organic mater. Over millions of years, this limestone has lifted out of the ocean from below sea level, to 4,144 feet in elevation at a rate of about two inches every year. It takes an incredibly slow rate to move the fault that it is close to impossible to see large changes over time. Now, I said close to impossible, meaning there are rare occasions that you can see great movement. An example would be a strong earthquake, a 7.0 or higher on the Richter scale and it can move up to 100 feet in a matter of minuets.
How Does Limestone Form?
Some segments of the San Andreas Fault are creeping (moving) segments and some are locked (static) segments. This segment you see in front of you is static and although it sounds good that the fault it not active here, it's the worst thing that could happen. A static fault can build up potential energy, or energy used for a potential action. This can build up so much pressure that a magnitude 7 earthquake can happen once every 100-150 years. We are way overdue. In contrast, a creeping segment moves constantly at a rate of about two inches per year. The San Andreas Fault has both segments and the locked segments are ironically located near California largest cities. See the map below.
Fault Movement Map
**NOTE** - You are at the near the intersection of the Garlock Fault, California's second longest fault line behind the San Andreas. The San Andreas runs 800 miles, while the Garlock fault runs about 200 miles. You are just past the tip of the arrow of the words, "You Are Here"
Works Cited
The following are my cited sources. I got the information from there, but did not copy.
http://geology.com/rocks/limestone.shtml
http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php
http://pubs.usgs.gov/gip/earthq3/safaultgip.html
http://pubs.usgs.gov/gip/dynamic/tectonics.html
http://www.earthquakecountry.info/roots/socal-faults.html
http://www.sharkbay.org/geological_foundations.aspx