Geological History of Nevada
The state of Nevada is situated in the southwestern mountaineous west of the United States. It is located west of Oregon, and Idaho, to the east, and west of California, and southwest of Arizona. The political authority area is divided into areas named Nevada County. Carson City is officially a consolidated municipality; however, it is considered a county for many purposes in the state system. In 1914, there were 17 counties in the state, ranging from 146 to 18,159 square miles.
History
Nevada's formation began around 3.5 million years ago. During Nevada's creation, five major events dominantly shaped Nevada's structure as we see it today.
The Great Nevada Meteor impact
In the Devonian period, more than 360 million years ago, Nevada's reefs were home to many marine creatures of the continental shelf in the shallow sea. They lived in the warm water because Nevada itself was a continental shelf.[1] One day, a large meteor, traveling faster than 20,000 miles per hour, fell in Nevada, 100 miles north of today's Las Vegas. Like landing in a hard pool, the Hypervelocity impact made a large splash in the sea as it ripped a chunk of the sea floor. A series of destructive tsunamis hit near Nevada. The resulting jumbled rock is called the Alamo Breccia. Ironically, Zero Point is found near Rachel on Nevada State Highway 375—nicknamed the Extraterrestrial Highway.
The big squeeze
A few decades after the Alamo Breccia impact, Pangaea began to break up into continents. This supercontinent had been intact for a long time, but eventually, it broke apart. Many aspects of Nevada's geology are linked to the fragmentation of Pangaea. As North America moved away from other continents, a part of the Pacific Ocean floor was forced to pull down Nevada's base and east of California, resulting in strong compression along the western margin of the North American continent.[2] Huge slabs of rock, each thousands of feet thick, were placed horizontally, separating into layers. The fossil-rich limestone deposited in the shallow zone was uplifted. For example, Charleston Peaks, with an elevation of around 12,000 feet above sea level, is mainly composed of fossiliferous marine limestone.[3]
The Eruption of Caldera
Hundreds of millions of years ago, Volcano Caldera exploded near present-day Hoover Dam, sending a thousand-foot column[clarification needed] into the sky. Simultaneously, from the erupting crater, a ground-hugging cloud rotating at one hundred miles per hour began its eruption.[1] It killed everything in its path, and the snowy landscape was buried under a layer of volcanic particles, a hundred feet thick. Volcanic ash resulted in the dark Black Canyon, which secures the Hoover Dam. If this had not happened, the recent human history of Southern Nevada would have been very different. Blue Canyon's Nevada wall is only visible below the Hoover Dam. Pink rocks are rhyolitic ash flows from the caldera volcano, which collapsed 13.9 million years ago.[2] The discontinuous dark band (composed of basaltic andesite), which cuts through the pink rock, is called a sill. Thick rock magma intensely intruded into the ash. This was the result of another explosion 1.2 million years later, from a nearby volcano. After much erosion, the thick integrated volcanic deposits consolidated.[1]
The Sierra Nevada's Pulse of Uplift
The Mojave Desert is prominent in southern Nevada, while central and northern Nevada are within the higher Great Basin Desert. This desert ecosystem owes its existence to the Sierra Nevada mountain range.[2] As moisture-rich air masses travel from the Pacific Ocean, they cross the Sierra Nevada and lose their moisture. This Sierra Nevada 'Rain Shadow' arose around 3.5 million years ago, when the mountain range experienced a sharp pulse of uplift. Without this uplift, Nevada would be wet and densely forested today.[2]
The Extinction of Nevada's Ice Age Megafauna
During the Pleistocene Ice Age, 10,000 years ago, Nevada was populated by a diversity of large animals: mammoths, camels, bison, horses, giant ground sloths, Saber-toothed cats, and dire wolves, among others.[4] Unusual central Nevada geologic terranes, Forrest G. Poole and Charles A. Sandberg, 2015.</ref> Most of these creatures went extinct within a few hundred years, causing a dramatic change in North America's ecosystem.[4] Mojave Desert plants, such as Joshua trees, were also affected. The extinction of these flora and fauna disrupted the Mojave Desert ecosystem, which scientists still do not fully understand.
Geology of Nevada
Nevada's geology is fundamental to its natural resources and is closely tied to human history. The state's complex geological history impacts its minerals, water, and energy resources; environmental issues; and inherent dangers. Nevada is characterized by numerous mountain ranges, usually 10 miles wide and less than 80 miles long, separated by valleys. Faults dominate the geologic structure that controls this basin-and-range topography. Almost every mountain range is bordered by at least one active fault, with significant earthquakes occurring within the last 1.6 million years.[3] These faults have been active for several million years, sometimes tilting mountains and basins. Erosion fills these basins with sediments derived from the mountains, resulting in deposits thousands of feet thick. Many range-bounding faults remain active. Nevada is the third most seismically active state in the nation; in the last 150 years, a magnitude 7 or greater earthquake has occurred approximately every 30 years. Faults are often normal, although some strike-slip faults exist. The most obvious area of strike-slip faults in Nevada is a 50-mile-wide zone along the northwestern border with California. These northwestern faults accommodate the motion of the Pacific Plate, moving relatively northwest, and the North American Plate, moving relatively southeast.
The Rocks of Nevada
Nevada's geological history documents extensive volcanic and intrusive activity. Nevada's igneous rocks spread across the sea floor 450 million years ago (similar to the mid-oceanic ridge or the East Pacific Rise today). Collisions of ancient and modern plates created the connection between Nevada's igneous rocks and the ocean floor.[3] Some of Nevada's volcanic rocks may be associated with the Yellowstone Hotspot, which resulted from plate tectonics beneath it, and produced volcanoes in Southern Idaho and northern Nevada.[4] Often, but not always, ore reserves in Nevada are related to igneous activity. In some cases, the metals themselves originated from magmas. In other cases, magmatic heat drove the circulation of warm water, leading to mineral deposition in veins within fractured sedimentary rocks. Some minerals were deposited when magma intruded and metamorphosed sedimentary rocks. Even today, deep circulation along faults, and likely locally driven by igneous activity, produces hot water in many geothermal areas. Some rocks contain Devonian Cambridge Carbonate Shelf deposits, including limestone, dolomite, sandstone, shale, and quartzite. This is similar to the "eastern assemblage" of Roberts et al. (1958) and the "carbonate assemblage" of Stewart and Carlson (1978).[4]
Mining in Nevada
Mining plays a major role in the state's economy, except for Las Vegas and Reno. Gold is the most important mineral by value. In 2004, 6,800,000 ounces (190,000,000 g) of gold valued at $2.84 billion accounted for 8.7% of the state's gold production. Other minerals mined in Nevada include materials used in building construction, copper, gypsum, diatomite, and lithium. Despite its mineral wealth, mining costs are generally high, and production is susceptible to global pricing. Nevada is the leading state in gold, barite, diatomite, and mercury production and is currently the only state that produces magnesite, lithium, and certain clays, including sepiolite and saponite. Nevada is also a leading producer of geothermal power and gypsum. Metal deposits are mainly related to volcanic activity, with major intrusions occurring during the Jurassic, Cretaceous, and Tertiary periods. Paleozoic sedimentary rocks are abundant in gypsum and barite. Lithium is extracted from brines beneath large playas. Quaternary faults play a vital role in geothermal power production.[3]
Landscape of Nevada
Nevada displays a distinctive mosaic landscape. Across its vast expanse, flat valleys are interrupted by mountain ranges. The basins and foothills that surround them show widespread evidence of aridity. [1] The mountains that remade America: how sierra Nevada Geology Impacts Modern life , Craig H.Jones, 2017</ref> However, the mountains are very high, with conifer forests, snow-covered peaks, and even some glaciers.
The Great basin
All of Nevada is part of the Great Basin. Nevada's basin and range province, predominantly oriented north-to-south, differs from the similarly oriented valleys of linear mountain ranges dominating the southwest.[5] It is the product of continental extension, pulling the continental crust apart and creating related faults. Many arid basins, often 4,000 feet or higher, contained ponds during the wetter climate of the Pleistocene.[1] However, they are mostly dry and alkaline flats and sagebrush steppe.[1] Sediments eroded from the mountains spread into the valleys, often in brief, intense floods. Where many alluvial fans merge, they form a pedestal-like landform called a "bajada". Fault-block mountains reach 13,000 feet in some ranges, exhibiting glacial features such as horns, knife-edge ridges, amphitheater-headed valleys, and other distinctive landforms. The highest point in Nevada is 13,063-foot Wheeler Peak, in the Snake Range, which supports one of the southernmost glaciers in the country.[1]
Mojave Desert
The Mojave Desert covers southern Nevada, forming a transition zone between the colder, higher Great Basin Desert to the north and the hotter Sonoran Desert to the south. Like the two deserts, this basin and range province exhibits a distinctive topography of isolated mountain ranges and level basins. Scattered shrubs dominate the ecological form in most of the Mojave, with the iconic Joshua tree prominent across much of the region.[1]
Sierra Nevada
A small portion of Nevada's western border lies within the Sierra Nevada, a 400-kilometer mountain range primarily located in California. While the western slope of the Sierra Nevada rises gradually from the Central Valley, the eastern front is steep and abrupt, creating a dramatic drop into the Great Basin. Lake Tahoe, shared with California, lies in a fault basin between the central spine of the Sierra Nevada and a spur, the Carson Range.
Mountains of Nevada
Nevada is a mountainous state. During mountain formation, extensive tectonic activity, including uplift and subduction, resulted in the dominance of horst and Graben structures in Nevada's mountains.
References
This article "Geological History of Nevada" is from Wikipedia. The list of its authors can be seen in its historical and/or the page Edithistory:Geological History of Nevada. Articles copied from Draft Namespace on Wikipedia could be seen on the Draft Namespace of Wikipedia and not main one.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 [https://pubs.er.usgs.gov/publication/70193220 Unusual central Nevada geologic terranes produced by Late Devonian Antler orogeny and Alamo impact, Forrest G. Poole and Charles A. Sandberg, 2015.
- ↑ 2.0 2.1 2.2 2.3 The mountains that remade America: how sierra Nevada Geology Impacts Modern life , Craig H.Jones, 2017
- ↑ 3.0 3.1 3.2 3.3 Geology of Nevada, Jonathan .G. Price, 2003
- ↑ 4.0 4.1 4.2 4.3 Geologic Maps of Nevada, A. Elizabeth Jones Crafford, 2007.
- ↑ The great basin: a natural prehistory, Donald K Grayson, 2011.
