This week I have traveled to Lake Tahoe in Placer County, California. The lake and surrounding mountains have been formed by extensive change over a geological time frame. To examine the area and understand the processes involved, the geological data from the California Geological Survey is a prime source.
The Tahoe area is a complex geological story, formed over millions of years. For example, the below rock is an igneous injection, formed by some long ago volcano. That volcano is gone and the rock was eventually exposed by erosion, picked up by a glacier and deposited here, some 6 km away.
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| Source: https://www.earthmagazine.org/article/travels-geology-lake-tahoe-jewel-sierra-nevada |
The Geological Survey is helpful when studying the area. Once the sediment layers and ages are understood using this data, the history of uplift and faulting can be understood. The Principal of Original Horizontality tells us that the layers of sediment were originally placed in horizontal stacks. After these stacks broke, eroded away or were cut by glaciers, the process of correlating the layers helps Geologists understand the changes over Geologic time.
A map of the faults would be useful, also. Sometimes faults that are not exposed may be difficult to see, so a map of previous discoveries can help interpretation of a site. Resources on the watershed and water history is useful, as well. Since erosion is such a powerful force over geological time, resources that can share information on the past forces will be helpful.
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