Welcome to the Tejon Pass! I had an earthcache here before, but it got archived. So I am redoing it with a much more in-depth analyis. At this point, you at the highest point along Interstate 5 in the Tejon Pass at 4,144 feet in elevation. This area can get snow in the winter, and fires in the summer and both have happened before. Parking can be found only along the bridge and not Peace Valley Rd. At the above coordinates, you will witness a rare geologic site. There is a clear distinction between two techtonic plates at this outcrop. Something not seen too often with the San Andreas Fault, especially the southern San Andreas Fault.
Before I go into any more details lets first discuss the basic fundamentals of how fault lines (or zones as they are refered to in the scientific community) are created and how 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. The hotter liquid is less dence as the molecules push out more than the dencer ones, which are colder. 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 zone is created.
Now at this point I'm sure you are asking, "What is a fault zone?" Well, it is place where two blocks are offset with one another. The intersection of these two blocks is a fracture called a fault. The largest faults are defined by the plate boundaries of the Earth, however faults can happen at any scale. Both macro and microscopic. The two blocks build up stress at differen rates which causes the rock to fracture and release that built up energy. This is called an earthquake. This friction is formed by these convection currents. When they move in a circular pattern in one direction, they can push rock with them.
Depending on the pressure, it can create a negative magnitude earthquake on the Richter Scale or all the way up to a 10. Yes you heard that right, a negiative maganitude! These are nearly constant occurances and are barley deteicable by modern day equipment. 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, what is special about this particular earthcache? At this location, you can see two different tectonic plates that the San Andreas Fault separates. To the north of the fault zone, at 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, and Hawaii before reaching the Mariana Trench near Japan. Here, you can easily see the two individual plates by the difference in color. The Pacific plate is on top in white rocks (limestone) and the North American plate in red just below it (mudstone). 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. Limestone forms as a result of calcium-rich sea life as that associated with a warm shallow sea located near the tropics. The type of sea life are usually those with shells made up of calcium carbonate. When the animal dies, thier shells compact and cement into limestone. Limestone gets its distinctive color from the calcium in the rock. 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 several milimeters per year (vertically). The San Andreas Fault has moved this horizontally at a rate of 2 inches per year, although this motion only occurs during large earthquakes. The last time this part of the San Andreas Fault ruptures was in 1857 during the 7.9-8.3 Fort Tejon Earthquake.
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 very active here on a day to day basis, 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 or larger earthquake can happen once every 100-150 years. We are way overdue, with the last large earthquake occuring here in 1857. 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.
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER ALL THE QUESTIONS BELOW. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER TO SEND YOUR ANSWERS. ANY INCORRECT ANSWERS MAY RESULT IN A CLARIFICATION RESPONSE FROM ME.
1. San Andreas Fault - Tejon Pass (2.0) on the first line of your email.
2. Take a close-up picture of the San Andreas Fault (contact between the two different rock units) using some sort of scale. Geologist sometimes use coins, books, or even humans! Be creative in what you choose for your scale. Note: this is not a selfie, but rather a documentation of the geology using a scale. Additionally, this is a rare site where geologist can definitively see a clear distinction between two tectonic plates on a small scale along the Southern San Andreas Fault. Normally, the fault forms a zone (a series of lines) but here it forms a single, distinctive line. Each log must have a unique and different photo. No two logs may contain the same photo.
3. Note the elevation noted on your GPS. What would you expect the elevation to be at in (a) 1,000 years and (b) 1,000,000 years?
4. Estimate the angle of elevation of the fault. 180° is completely flat, 90° is a right angle etc. Note that the examples noted here are not the answers.
5. As stated in the description above, the white in limestone of the Pacific Plate is formed from marine life over millions of years. What do you think could have caused the reddish orange color of the North American Plate? Hint: Think about what environment this formed it.