You can find parking to the north or to the south. If you choose to park at Torrey Pines State Preserve (north of the cache) the current parking fees (as of 28Jul2012) are: $12 Mon-Thurs, $15 Fri-Sun and Holidays. If you are coming from the north and walking south, check the tides as there is one location that may becomes impassable at high tide.
The coordinates bring you up to the Carmel Valley fault. A fault is a fracture in a rock that shows movement. The evidence of movement along this fault can be seen by examining the elevation of the same rock layers on either side of the fault.
As you look at the cliff the fault is located underneath the sand eroded down the channel cut into the cliff. It cuts across the rock at a slight angle from lower left to upper right. On the south (right) side near the base of the cliff is a gray-green mud and siltstone called the Del Mar Formation. Above the Del Mar Formation is the Torrey Sandstone a white (but often stained light brown) rock. On the north (left) side of the fault only the Torrey Sandstone can be seen. As you try to trace the contact between the Del Mar Formation and Torrey Sandstone from right to left, it is cut off by the fault.
From the fault begin walking north watching the base of the cliff for the Del Mar formation. Keep track of how far you walk as this is part of the logging requirement. Once you see the gray-green mud and siltstone at the base of the cliff again, notice that the contact between the Del Mar Formation and Torrey Sandstone seems to gradually comes up out of the sand at a slight incline. More and more of the Del Mar Formation is visible to the north. Back to the south, you will have to imagine the contact between these two layers continuing down underneath the sand of the beach until it reaches the fault. Thus the Del Mar Formation is lower on the left side of the fault than it is on the right side of the fault.
Remember that the fault is not vertical but leans slightly to the south. You can picture the fault like a giant slide. The rocks on the left have slid down the slide in the normal direction that gravity would pull something sitting on the slide. This type of fault is called a normal fault.
Since faults are breaks in the rocks, they tend to be weakest area of the rock.
This fault is also exposed along the road cut east of here along Old Highway 101 near N32 55.133 W117 14.933. The better parking is from the northbound lanes as you come down the hill. For the extra credit post a picture of the fault along the road and send me the coordinates of the location where you took the picture. (Do not try to cross the road on foot.)
Send me a note with :
- The text "GCZ68Z Carmel Valley Fault – Torrey Pines SR" on the first line
- The number of people in your group.
- The distance between the fault and where the Del Mar Formation is first exposed north of the fault at the base of the cliff. (Extra credit for calculating the approximate depth of the Del Mar Formation at the fault. You can assume the contact between Del Mar Formation and the Torrey Pines Sandstone hits the fault at 90 degrees)
- Your explanation as to why there is so much material covering the fault at the base of the cliff.
The above information was compiled from the following sources:
- Geology of Torrey Pines State Reserve By Don Grine, Geophysicist Emeritus, Torrey Pines State Reserve 2006, http://www.torreypine.org/geology/geology.html#rock
- Image from USGS