The Barstow Syncline in Rainbow Basin

Rainbow Basin National Natural Landmark is a fascinating area located near Barstow, California. It’s an area of high hills, deep canyons, and much more. One of its most well-known features is the textbook example Barstow Syncline.

Here’s the view of the Barstow Syncline from the overlook across the mouth of Rainbow Canyon.

Barstow Syncline

As any neophyte structual geologist knows, synclines are downward curving folds with anticlines their opposite. I’ve always remembered this by associating synclines with “sinks” and anticlines with an “A” shape. In synclines the downward dipping layers point towards the middle of the structure, and they’re obvious in the photo above.

The Barstow Syncline is especially interesting since it also clearly shows an unconformity across its top. Uncomformities are strata of different ages that are in contact, indicating non-continuous deposition and a break in the geologic history of the layers. In this case the uncomformity was created as the syncline was eroded and younger layers were subsequently deposited uncomformably above it. Erosion has revealed the entire structure for all to admire.


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