8: Basin and Range
- Page ID
- 20342
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Introduction
The Basin and Range Province is situated in easternmost California (Figure \(\PageIndex{1}\)) and is probably one of the most important natural geologic laboratories in the world. Because of its lack of vegetation and the long span of geologic time that is represented in this region, scientists from all over the world have used this area to formulate and test their geologic hypotheses. Important studies emerging from this region have produced tectonic reconstructions of the western U.S., proposals of an ancient “snowball earth” and a new understanding of the ways Earth’s crust behaves during mountain building! This region is also the home of Death Valley National Park and the focal point of water rights and land use controversies that have been evolving for centuries.
The geologic story of the Basin and Range is a long one, going back to the Middle Proterozoic Eon. Its most recent history, however, is one of continental rifting, which has produced the distinctive “basin and range” structures for which this region is named, along with volcanism caused by crustal thinning. Widespread normal faulting caused by this rifting has exposed old rocks (including some of the oldest found in California) in uplifted footwall blocks, making it possible to study the earlier history of this region. Geologic activity also continues today: ongoing seismic and magmatic activity present not only serious hazards in the region, but also important geothermal resources and create a dynamic landscape with a lot to interest geologists.
There is plenty of geology to discuss in this region and it would be impossible to complete this study in a one semester course. This chapter will, instead, aim to provide an introduction to a few key aspects of the region and lay the groundwork for future study and examination as your interests guide you. In particular, our focus will be on the concept of continental rifting illustrated with examples from the Death Valley and Owens Valley regions, including some of the hazards and benefits resulting from this rift environment. The chapter will conclude with a discussion of some of the bedrock geology that was exposed by this rifting and the insights it provides about the geologic past.
- Locate the Basin and Range Province on a map of California.
- Describe the primary geomorphic features in the Basin and Range Province.
- Recall the major geologic units in this province as presented on a simplified map of California.
- Explain the origin of the “basin and range” structures in this geomorphic province.
- Outline the evidence for ongoing seismic hazard in this geomorphic province.
- Summarize the geologic evidence for continental rifting in the Basin and Range Province.
- Explain the origin of rift-related volcanic features found in this region and their associated hazards and benefits.
- Summarize the evidence for Late Proterozoic rifting and glaciation in this region.
- 8.1: Regional Extent and Overview of the Basin and Range
- The Basin and Range of California is part of a much larger continental rift zone that extends to Utah and south to Mexico. Lying in the rain-shadow of the Sierra Nevada mountains to the west, this arid region is known for its linear fault bounded ranges and basins, as well as geology that spans a wide range of geologic time and represents a range of geologic environments.
- 8.2: Rifting in the Basin and Range
- The primary geological highlight of the Basin and Range Province is the impact of continental rifting which has been superimposed on older geologic features. Continental rifting, one of the stages of the Wilson Cycle, begins when a region is under tension. The Basin and Range Province of California a broad continental rift zone that developed along with the formation of the present-day transform plate boundary to the west. Although this region has not yet begun to create oceanic crust, there are
- 8.3: Rift-Related Faulting in Eastern California
- The Basin and Range Province contains a large number of normal faults that formed in response to continental rifting. They have produced a series of uplifted ranges (the footwalls of normal faults) and basins (the down-dropped hanging walls). This section discusses the formation of these features and the ongoing hazards that they present for those who live in the region.
- 8.4: Sedimentary Products of Rifting in the Basin and Range
- Sediments shed from uplifted fault blocks preserve the history of basin formation. Shallow seasonal lakes that form in many of the basins are the remnant of much large lakes but have been reduced due to climate change and diversion by the City of Los Angeles. Desiccation of these lakes is recorded in the geology and presents a pollution hazard for residents.
- 8.5: Rift-Related Volcanism in Eastern California
- An important byproduct of continental rifting is volcanism that goes along with it. This section will discuss the causes of that volcanism, and review some of the features that are found in this region. Of interest is the Long Valley Caldera, located to the east of the Sierra Nevada Range. For a review of volcanic products, see the chapter on Rocks and Minerals.
- 8.6: The Oldest Rocks in the Basin and Range
- The oldest rocks in the Basin and Range Province, dating to 1.7 Ga, are exposed in ranges bounded by normal faults and record the rifting of Rodinia, as well as evidence for the “snowball earth”. Most of the Paleozoic rocks in the region are associated with the development of a passive margin following rifting. The Snowball Earth refers to global glaciation during the Neoproterozoic era. Evidence for rifting and glaciation are found in the oldest sedimentary rocks of this region.
- 8.7: Chapter Summary and Key Terms
- A summary of highlights from each chapter.