9: Sierra Nevada
- Page ID
- 20343
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The Sierra Nevada province is a 644 km-long (400 mile) 80 km-wide (50 mile) region trending north-northwest and located primarily in central and eastern California. A small spur of the province called the Carson Range is just over the border in Nevada. It is bounded by the Cascade province to the north, the Basin and Range province to the east, and the Great Valley province to the west. The Garlock fault forms the southern boundary of of the Sierra Nevada province, separating it from the Mojave province (Figure \(\PageIndex{1}\))
The most prominent feature of the Sierra Nevada province is its mountain range of the same name which boasts notable features such as the highest peak in the contiguous United States, Mount Whitney at 4,421 m (14,505 ft); Yosemite Valley and National Park; and Lake Tahoe, the largest alpine lake in North America.
The Sierra Nevada range of California has a complex geologic history that spans 210 million years. While the majority of what would become the Sierra Nevada Province started forming during the Mesozoic Era, what we see today did not exist and is very different from the Sierra Nevada of that time.
The Sierra Nevada Mountains began to form when a series of intrusive plutonic events began to formed much of the range's granitic rock, including iconic features like Half Dome and El Capitan in Yosemite National Park. Over time, erosion and crustal extension gradually revealed plutonic granite formations at Earth's surface. Tectonic forces continued to uplift the emerging Sierra Nevada range, shaping it into the distinctive landscape we observe today.
During the Cenozoic Era, tectonic forces continued to uplift the Sierra Nevada, and the mountains were sculpted by glaciers during the Pleistocene, giving rise to the dramatic landscapes seen today.
This chapter explores the history of this region, including the emplacement, exhumation, and erosion of batholiths - magma chambers that fed a once extensive volcanic arc, the accumulation of gold deposits that would make the Sierra Nevada famous in recent times, and glacial evidence attesting to a changing climate in this region.
By the end of this chapter, you should be able to:
- Describe the Sierra Nevada province in terms of rock types, age, and tectonic development.
- Assess the geologic hazards and risks associated with the Sierra Nevada province.
- Describe the geologic processes involved the formation and preservation of gold.
- 9.1: The Sierra Nevada Today
- The primary geologic feature in this province is the magnificent Sierra Nevada Mountains. This range is underlain by felsic to intermediate granitic rocks and metamorphosed sediments. The range is gently sloped to the west, with a steep eastern face that is bounded by the Sierra Nevada fault. Elevations range from ~2,700 to ~4,300 meters (9,000 to 12,000 feet), with the highest peaks found in the southern part of the range. Here, Mount Whitney (elevation 14,496 ft; 4,418 m) rises more than 10,00
- 9.2: Ancient Seas Form the Oldest Rocks
- For over 500 million years, marine sediments accumulated, forming a record of the ancient environment. These sediments, mostly marine, indicate formation in a shallow sea, with the eastern Sierra closer to shore. Beyond the continent, island arcs similar to today's Aleutian islands existed, foreshadowing the future California and Sierra Nevada. From such ancient seas from the oldest rocks of the Sierra Nevada.
- 9.3: The Sierra Nevada Batholith
- The geology of the Sierra Nevada Province is dominated by the plutonic rocks of the extensive Sierra Nevada batholith, along with the metasedimentary and volcanic rocks into which they intrude. The overall geologic trends parallel the range and provide exposure of the roots of an ancient magmatic arc along with the accreted metamorphic belts that were thrust onto them.
- 9.4: Gold of the Sierra Nevada
- Nestled within the geological tapestry of California lies a treasure that has shaped both the landscape and human history: gold. Renowned as the state mineral, gold embodies the intricate interplay of geological processes that have sculpted the rugged terrain of the Sierra Nevada and fueled the aspirations of generations.
- 9.5: Volcanic Features of the Sierra Nevada
- The Sierra Nevada features younger volcanic formations, like the Mono-Inyo Craters, which resulted from recent tectonic activity linked to the Basin and Range Province. This activity caused the crust to stretch and magma to rise, forming rhyolitic domes, craters, and lava flows, with the latest eruptions occurring about 600 years ago.
- 9.6: Ice Shapes the Landscape
- Glaciers in the Sierra Nevada formed during the Pleistocene, when cold temperatures allowed snow to accumulate and compact into ice. High elevations and steep terrain, especially in Yosemite and Kings Canyon, were ideal for glacier formation, carving deep valleys and peaks. As glaciers advanced and retreated, they left behind deposits that help geologists trace their history and influence on the landscape.
- 9.7: Natural Hazards of the Sierra Nevada
- In exploring the Sierra Nevada region, it becomes evident that its breathtaking beauty is accompanied by a complex array of geologic hazards. From the rumblings of seismic activity to the cascading threat of landslides, this majestic landscape harbors a myriad of natural dangers. Nestled within its rugged terrain, earthquakes, landslides, rock falls, flooding, and volcanic activity intertwine, each presenting its own unique challenge to those who call this region home.
- 9.8: Chapter Summary
- Summary of key chapter points and items related to the Sierra Nevada Province.