Note: the yellow box is enlarged in the next diagram
The Big Bend in California Geology refers to the bend of the San Andreas Fault. The fault itself is not necessarily a straight line, but for the most part to the north and south of this section it is. The San Andreas Fault isn't the only fault that's contributing to this feature. The Garlock and Big Pines fault also play a major role. In order to understand how these faults are effected by this geologic feature, you must understand what a fault zone is and how they function fundamentally. 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's more of a fault zone since it's a collection of cracks rather than one single crack. Simplicity, 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. Now that you better understand faults in general, we can now discus the unique geologic principles that are in action at The Big Bend. It's best if you would refer to the diagram below as reading through the next few paragraphs.
Works Cited
As you can see above, there's an obvious bend in the San Andreas Fault. The Garlock Fault is to the north of the bend and the Big Pine Fault is to the south. At the time the Garlock Fault was first being created, the Big Pine Fault and the Garlock Fault were the same exact fault. Today, this gap is due to the offset of the San Andreas Fault and it has literally offset a fault zone. This can be better understood when you look at the relative motion of things in this area and knowing that there is more than just one type of transform or strike slip fault.
The North American Plate to the north is moving to the south relative to any fixed location. The Pacific Plate is moving to the north relative to any fixed location. The San Andreas Fault is the line that fills this difference, where two major tectonic plates meet. Because of this movement, the San Andreas Fault is classified as a right-latteral strike strip fault that moves an average of 20 to 30 centimeters per year. An easy was to know is to stand on one side of the fault and look to the opposite side. In this case, standing on the Pacific Plate, you look to the north to the North American Plate. The North American Plate is moving to the right relative to where you are standing, hence why the San Andreas Fault is a right-lateral strike strip fault. If the North American Plate was moving to the left, then it would be a left-lateral strike strip fault. The Garlock and Big Pine Faults are left-lateral strike strip faults which better backs up this evidence that they were part of the same fault when they first were created.
Because the faults here move in opposite directions, interesting things can occur. The south side of the Garlock Fault defines the Mojave Desert where the land is sinking because of the fault's opposite motions. If you have time, you can learn more about the creation of the Mojave Triangle (GC63YQD) at one of my earthcaches that's about 15 miles away from here. In the center of this bend of the San Andreas Fault there's compression. The land to the south is moving to the north and the land to the north is moving to the south. This is still technically a transform boundary, but for this small area acts as if it was a convergent plate boundary. It's the reason why the Tejon Pass is so high in elevation compared to all the other nearby passes such as the Cajon Pass, which also contains the San Andreas Fault. It's also the reason why the mountains are here are so wide, compared to the Cajon Pass. Lots of compression means lots of mountains. The Cajon Pass doesn't have a large bend because the fault there is relatively a straight line, hence it only takes about 20 minutes to drive from one side of the mountains to the other. Here, it normally takes about an hour before you get out of the mountains.
http://slideplayer.com/slide/5214361/
http://pubs.usgs.gov/gip/dynamic/tectonics.html
TO LOG A FIND ON THIS CACHE YOU MUST GIVE ME THE CORECT ANSWERS. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER. ANY INCORRECT ANSWERS WILL RESULT IN A DELETED LOG
1. "The 'Big' Bend" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. Note, this IS cheating as only the person who sent their answers has learned something, while the others get a "free ride". It's not fair to others. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching.
2. Given that the Garlock and Big Pine Fault were the same fault, estimate the age when the fault was connected into one. To calculate, you need to know the average rate movement of the San Andreas per year and the distance between these two separate faults. Use the diagrams above to help you calculate as well as the cache description. You may want to do this calculation at home. {Time x Rate = Distance (You are solving for time)}
3. Knowing the answer above, when will the Garlock and Big Pine Faults be (a) 50, (b) 100, (c) 250 miles apart?
4. How far does the Garlock Fault extend from this vantage point? Note: You are standing on it.
5. How far does the San Andreas Fault extend from this vantage point? Note: Your back must be facing Interstate 5.
6. Why can't you see the Big Pine Fault from here? Where would it be?