David Pilcher collected various rock samples in California to fulfill a geology assignment. He traveled to San Luis Obispo County to study metamorphic rocks formed by the San Andreas Fault. He found hornfels along the coastal mountain ranges. Sedimentary rocks were found along the central coast, including sandstone and conglomerate collected from beaches. Igneous granite samples were easily accessible in the Sierra Nevada foothills near volcanic rock formations resulting from the subduction of tectonic plates millions of years ago. Through field observations and comparisons to online resources, David was able to identify the different rock types and understand how they relate to California's geological history.
2. Field Observation and Collection California offers a wide range of geological specimens. At first I was concerned about how and where I was going to find these different rock types. Then after looking at some geological maps of California online, it did not take long to discover that these rocks can be found in a number of different places. It takes a good understanding on California’s geological history to complete this assignment.
3. Field Observation and Collection I ventured out to San Luis Obispo County for the first part of this assignment. There is a well known fault line called the San Andreas Fault in the coastal mountain ranges. It seemed like a good place to study geology, and observe rock formations.
4. Metamorphic As I have learned from this class metamorphic rocks are made from high temperatures, pressures, and chemical reactions. The San Andreas Fault is one of the major fault lines in between the Pacific and North American tectonic plates. Approximately 250 million years ago, the Pacific Plate met the Continental Plate of North America and the Pacific Plate slipped beneath the North American Plate. As the Pacific Plate started to reach the Earths interior it heated and melted. Around 150 million years ago, the magma started to surface creating igneous rock formations. Through further periods of heat, pressure, and chemical reactions, these igneous rocks transformed giving us examples of metamorphic rocks.
5. Field Observation and Collection While driving through the coastal range in Western California I made several stops and collected rocks. I believe this is a good example of a metamorphic rock. After researching geology.com, I believe that this is an example of hornfels.After comparing it to the pictures in the lecture notes I see the similarities in veins that can be found in the different types of metamorphic rocks.
6. Sedimentary Loose particulate matter that goes through compaction, cementation, and recrystallization forms sedimentary rocks. The rocks found in the Western United States are from the Mesozoic and Cenozoic time periods. I traveled to the coast line of California after reading that the water in the ocean can help the process of making some unique sedimentary rocks. We can use different colors in the rocks to help identify their origin as well as their makeup. For example black rocks can be a product of organic carbon and iron.
7. Sedimentary The two rocks to the left are both examples of Sedimentary Rocks. After looking at geology.com, I believe this is an example of Sandstone ( top) conglomerate (bottom) and They were collected on the beach on the central coast of California. They are completely different in appearance. The bottom rock almost appeared to be metamorphic, however it is soft and brittle, and was picked off the side of a small sediment “cliff” right behind the beach. The top rock has a higher sand content than the bottom, which makes if feel gritty
8. Sedimentary This rock to the right was a sedimentary rock that I had found in Parkfield, it appears to have been placed here but was a nice sample, and is most likley brought in from a local canyon. You can clearly see the different layers stacked on top of each-other as the rock formed over time.
9. Igneous Igneous rocks crystallized from hot, molten lava or magma as it cooled. Igneous rocks are the result of volcanic activity. The Sierra Nevada Mountain Range in California contains plenty of volcanic rocks, much more than the Coastal Range in our area. One of the most commonly found volcanic rock in the Sierra Nevada is granite. Like the Coastal range, the Sierra Nevada formed as a result of the Pacific Plate subducting below the North American Plate 250 million years ago. Then as the pacific plate heated and cooled volcanic plumes rose to the surface.
10. Igneous I collected a few samples of Granite from the Sierra Nevada Mountain Range. I didn’t have to travel very far. At the base of the mountain range in the foothills which contain plenty of examples. Both of these pictures are an example of granite.
11. References Lecture Notes Geology.com http://geology.com/ Textbooks: Tarbuck and Lutgens, Earth: An Introduction to Physical Geology, 10 th Edition, Prentice Hall (2011)
