Physiographic Provinces of California
The State of California comprises of 11 physiographic provinces; i.e., Basin and Range, Coast Ranges, Transverse Ranges, Peninsular Ranges, Cascade Ranges and Colorado Desert. The other physiographic provinces are the Great Valley, Klamath Mountains, Modoc Plateau, Mojave Desert and Sierra Nevada (GeologyCafe.com) (see fig 1 in the appendix). In this regard, Sierra Nevada is the major geological mainstay of California, comprising the largest mountainous system in the state (DeCourteen). The geological structure of this physiographic province is dominated by Sierra Nevada batholith, an enormous mass of granite rocks. These rocks were positioned on older rocks during Mesozoic period. Older metamorphic rocks surround Sierra Nevada batholith (“Northern California”10). Klamath Mountain is an elevated terrain, with an elevation ranging from 5000-7000 feet above sea level. This physiographic province has similar geological structure as the southern Sierra Nevada. The dominant rocks are older metamorphic and sedimentary bedrocks, formed during Precambrian, Paleozoic and Mesozoic era. The common geological processes in Klamath Mountain are erosion, weathering and graciation (“Northern California”12)
DeCourteen notes that the dominant geological structure in the Great Valley consists of quaternary Mesozoic and Cenozoic sedimentary rocks. Weathering and erosion are the dominant geological processes in this physiographic province. The geological structure of Coast Ranges is dominated by Mesozoic age mixture of sedimentary and metamorphic rocks. Geological processes in this region include faulting and erosion. Coast Ranges are characterized by San Andreas Fault system, which divides the physiographic province into northern and southern portions. Erosion is the predominant geological process in Coast Ranges causing a characteristic ruggedness on the northern Californian seaside. Spectacular coastal landforms such as marine terraces, sea stacks and sea arches have emerged in the Coast Ranges following the vigorous erosion (“Northern California”14-24).
According to DeCourteen, the geological structure of the Cascade Range is predominantly made up of tertiary and quaternary volcanic rocks. These volcanic features are relatively young and estimated to have formed from volcanic eruptions that occurred during the last 3 million years. Although earlier volcanic eruptions during Cenozoic era occurred, the resulting features have been hidden by the recent eruptions. Volcanic eruptions are the most common geological processes in cascade ranges. The dominant geological structure of Modoc Plateau comprises of tertiary and quaternary volcanic rocks. The plateau is lava plain that borders the Cascade Ranges and is elevated at about 4,500 feet, formed during volcanic eruptions in the last 3 million years. The region has active volcanic activity. Besides, the Basin and Range in northeastern California has alternating mountains and valleys. This physiographic province is made of tertiary and quaternary volcanic rocks, which erupted about 36 million years ago. Some of the influential geological processes in Basin and Range include faulting and volcanic activity. The Basin and Range in southern California, Mojave and Colorado deserts, are all arid regions, with similar geologic structures and at common geological stage (“Northern California”25-31).
DeCourteen further observes that Mojave Desert and Basin and Range in southern California comprise of sedimentary and older metamorphic rocks as the dominant geological structure. Colorado Desert is dominantly made of quaternary sediment rocks. These landforms were formed during Cenozoic, Precambrian, and Mesozoic eras. In this regard, Mesozoic igneous rocks are dominant geological structure in Peninsular Ranges. Transverse Ranges comprises of a highly complex rock formations, consisting of Precambrian metamorphic rocks, metamorphosed Paleozoic sedimentary rocks and Cenozoic sedimentary rocks (“Southern California” 28-35).
Geological Events Leading to the Formation of Visible Geological Features in California
DeCourteen lists several geological features in various physiographic provinces of California. These geological features include; batholiths, volcanoes, faults, basins and mountain ranges. Batholiths are important geological features in California. The Sierra Nevada batholith is a mass of granitic rock that was formed by the action of magma raising and solidifying into the crust. It was formed between 140 and 80 million years ago. During the formation of Sierra Nevada batholith, magma was produced Lin Farallon subduction zone and it moved upwards through older crustal material to build a series of volcanoes. The Sierra Nevada batholith consists of about 200 plutons (“Northern California”6).
San Andreas Fault system cuts across the northern Coast Ranges. According to DeCourteen, the fault was formed about 28 million years ago, when continuous westward movement of North American Plate caused the separation of triple junction between itself, Farallon and Pacific plates into two. The two triple junctions began moving in opposite directions along the continental margin. Following these movements, the pacific plate encountered the North American plate. However, due to the difference in movement and direction of these plates, a transform plate boundary was formed, as the two plates slid over each other. This transform boundary between North America and Pacific plates caused the development of San Andreas Fault system (“Northern California”21).
The continuous rise of the northern and southern Coast Ranges is another geological event that has resulted to formation of various geological features in California. DeCourteen notes that this geological event began 3 to 4 million years ago from a combination of geological events, including sedimentation and volcanic activity, where eruption of volcanic ash and lava was been deposited in the region increasing its elevation. The coastal mountains in northern California have recently emerged as land, demonstrating the raise of the northern coastal ranges (“Southern California” 21).
How Geology of California Affects the People
The geology of California has profound social economic impacts on the residents of the state and United States as a whole. According to DeCourteen, the Great Valley is one of the most agriculturally productive areas in the state, due to the fertile alluvial soils and abundant water. The value California agricultural amounts to an average of $32 billion annually and the Great Valley contributes a large proportion of this revenue. Sacramento valley for instance is a key food basket, producing key foodstuffs, such as rice, grapes, feed grains, orchard fruits and almonds in addition to walnuts (“Northern California” 15). However, in spite of its high agricultural production, Sacramento valley is a flood prone region due to its flat terrain and large volume of water from Sacramento River. The increasing human settlements in the region and intensive agricultural practices have particularly heightened the flood hazard in the region. In spite of the heavy investments that the state has committed to flood mitigation measures, the threat of flooding still persists.
The Cascade Range and Modoc plateau are young geological features and the pose significant volcanic hazard to the population. According to DeCourteen, Mount Lassen recorded a series of eruptions between 1914 and 1921. Mount Shasta and Medicine Lake are other volcanoes posing serious volcanic hazard to Californians having recorded recent eruptions. Volcanic activity poses serious health hazards by producing harmful gaseous emissions, destructive lava and particulate matter that cloud the sky, limiting visibility and causing serious respiratory diseases (29). San Andreas Fault system is another geological hazard, associated with earthquakes in northern California. The destructive 1906 San Francisco earthquake happened along San Andreas Fault line (“Northern California 28-34). Future earthquakes and seismic disturbances are certain in this dynamic tectonic region in northern California. The dense human settlements and heavy infrastructure in California are certainly in danger of destruction from powerful earthquakes and tremors.
Works cited
DeCourteen, Frank. “Northern California: Geology of Northern California”. Cengage Learning n.d. Web. 25 April 2013. <http://www.cengage.com/custom/enrichment_modules/data/0495763829_Northern%20Cali_LowRes.pdf>
DeCourteen, Frank. “Southern California: Geology of Southern California”. Grossmont. ed., n.d. Web. 25 April 2013. http://www.grossmont.edu/garyjacobson/Naural%20History%20150/Geology%20of%20Southern%20California.pdf
GeologyCafe.com. Physiographic Provinces Map of California. US Geological Survey, n.d. Web. 26 April 2013. <http ://geologycafe.com/california/maps/provinces_B&W2.htm>
Appendix
Fig 1: Physiographic Provinces of California
Source: GeologyCafe.com.
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