Geological Formation of the Rainbow Basin

Regional Geologic Setting of Rainbow Basin

The Rainbow Basin is located in the Calico Peaks in the Mojave Desert. The nature of the Mojave extension consists of sediments that were folded within the Barstow Syncline. The Basin is 8 miles to the north of Barstow where "Mud Hills" can be seen -- so-called because of the clay in the rock. Fossils are plentiful in the region, the remnants of life from the Miocene, along with plant remains, suggesting that the region was a coastal region in the past. The Basin itself gets its name from the colorful rocks -- whites, reds, greens, browns -- that come from the mineral deposits therein. Mudstone and sandstone make up most of the rock formations. The green coloring comes from the clay, while the white coloring is the effect of ash from volcanic activity on the Calico fault, which moves like the San Andreas fault. Its composition is rhyolitic.

The Garlock fault lies to the north of the Rainbow Basin. The San Andreas fault is to the southwest. The Basin is characterized by a badland type of topography. Extensive batholiths can be found beneath the sedimentary rock in the Basin, consisting of Cretaceous quartz monzonite layer (U.S. Department of the Interior 29).

The geology of the Basin was formed primarily in the Cenozoic era. The surface land was compressed into a bowl-shaped basin, where sedimentary and volcanic rock settled. The Rainbow Basin soil is mainly clay -- thus, there is hardly any vegetation that can grow.

The major regional geologic features of the Rainbow Basin are its badland type of features and its colorful mud-clay hills, which formed as a result of erosion -- the clay expanding following rains and giving the area a "muddy" look that is also colorful due to minerals in the clay. Its "perfectly exposed syncline and fault" is exposed along with "slot gorges" and "Miocene mammal fossils" (Hasbargen 23).

The tectonic setting of Rainbow Basin is situated between the San Andreas fault and the Garlock fault, and much shifting over the years has resulted in volcanic activity, which is evidenced by the ashen exterior and the volcanic cylindrical shapes that punctuate the region.

The location of Rainbow Basin within the Mojave desert is in the western portion of the desert. The famous Barstow Syncline can be seen, with the Jackhammer Formation visible at the lowest layer. It consists of limestone, siltstone, sandstone and conglomerate rock. Over this Formation is the Pickhandle Formation, which consists of volcanic rock. The top layer is the Barstow Formation, which consists of shale, sandstone, limestone and conglomerate rock. A thin fanglomerate covers the Barstow Formationi (U.S. Department of the Interior 30).

The Rainbow Basin is especially interesting because of its fossil beds which house ancient fossils and tell a story of the region that is very old. However, it is also a region for sightseeing: Coon, Owl and Fossil Canyons are places where vegetation does grow and where birds will congregate.

The diversity of the terrain is overall one of its most outstanding features and this is due to the collection of volcanic activity, its coastal properties from former eras, and its soil composition. The fault lines that essentially surround it have also added to the stress and pressure that has resulted in the Basin's unique formations, color, and features that attract visitors.

Works Cited

Hasbargen, Les. "Mojave-Mecca Geology Field Trip Guide Book." Oneonta, 2010.

Web. 23 Sep 2016.

U.S. Department of the Interior. Management Plan for the Rainbow Basin Natural Area.

CA: Barstow Resource Area, 1990. Print.