6: A Brief Geologic History of California
- Page ID
- 20339
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Geologists are historians that have a story to tell that is incredibly broad in both space and time. Geologists are also detectives that must search for the evidence and clues to the tectonic past. Often, subsequent geologic events obscure the evidence we are looking for in many ways: rocks are buried and no longer exposed at the surface, rocks are metamorphosed and may no longer look like the original rocks or have the same chemistry, tectonic processes can transport rocks great distances so they are no longer in the same place where they formed, subduction zones can return entire ocean basins to the mantle well beyond our view. While these physical and chemical changes obscure the original properties of the rocks, they are part of the story of how the rocks came to be where we see them today. Geologists are trained to identify these changes to rocks and what they mean about the environment the rock was formed in. Geologists then put these environments and events in chronological order based on cross cutting relationships or absolute ages.
In this chapter we will look at a broad overview of how the tectonic plates interacting along the western margin of North America have changed through time. We will also look at time slices of the geologic map of California to see how the geologic environment has changed through time and understand the evidence used to unravel the geologic past.
Table \(\PageIndex{1}\) summarizes the major geologic events that shaped California into what we see today. Like many geologic timescales, this table is organized with the oldest events at the bottom and youngest events at the top. This chapter presents a chronologic account of these major geologic events with each of the following pages detailing a different geologic era. This chapter acts as the temporal link between the various geological provinces presented in the following chapters. For more detailed information on the geology of a specific region, consult the relevant geomorphic province chapter.
| Era | Period | Epoch | Major Geologic Events in California |
|---|---|---|---|
| Cenozoic (66 Ma to present) | Quaternary (3 Ma to present) | Holocene (12 ka to present) | |
| Pleistocene (3 Ma to 12 ka) |
Ice age glaciers carve the Sierra Nevada and Klamath Mountains. Lakes flood the valleys in Modoc Plateau and Basin and Range. High Cascades volcanoes erupt. |
||
| Neogene (23 to 3 Ma) | Pliocene (5 to 3 Ma) |
Sutter Buttes volcanoes erupt. Sediments eroded from the Sierra Nevada and Coast Range are deposited into the Great Valley. |
|
| Miocene (23 to 5 Ma) |
Flood basalts cover the Modoc Plateau. Basin and Range extension begins. |
||
| Paleogene (66 to 23 Ma) | Oligocene (34 to 23 Ma) | Spreading center is subducted and the San Andreas Fault begins to develop. | |
| Eocene (56 to 34 Ma) | Laramide Orogeny ends. | ||
| Paleocene (66 to 56 Ma) | |||
| Mesozoic (251 to 66 Ma) | Cretaceous (143 to 6 Ma) |
Sierra Nevada sediments begin to fill Great Valley Klamath terrane accretes onto N. America Laramide Orogeny begins |
|
| Jurassic (201 to 143 Ma) |
Sevier Orogeny Nevadan Orogeny Supercontinent Pangaea begins to rift apart Sonoma Orogeny |
||
| Triassic (252 to 201 Ma) | Subduction of the Farallon plate begins. | ||
| Paleozoic (539 to 251 Ma) | Permian (299 to 252 Ma) | Calaveras complex rocks are deposited on the ocean floor. | |
| Pennsylvanian (323 to 299 Ma) | |||
| Mississippian (359 to 323 Ma) | Antler Orogeny deforms accreted rocks into tightly folded Shoo Fly complex. | ||
| Devonian (420 to 359 Ma) | |||
| Silurian (443 to 485 Ma) | |||
| Ordovician (487 to 443 Ma) | Trinity ophiolite forms. | ||
| Cambrian (539 to 487 Ma) | |||
| Proterozoic (2,500 to 539 Ma) | Neoproterozoic (1,000 to 539 Ma) | Supercontinent Rodinia begins to rift apart. Beginning of passive margin. | |
| Mesoproterozoic (1,600 to 1,000 Ma) | Abundant carbonate rocks form off the coast. | ||
| Paleoproterozoic (2,500 to 1,600 Ma) | Oldest rocks in California form. | ||
| Archean (4.0 to 2.5 Ga) | Ancient North American continent craton formed east of California. |
The dates on the table above are based on v2023/09 of the International Chronostratigraphic Chart from the International Commission on Stratigraphy. The latest version can be found on the ICS website.
By the end of this chapter, you should be able to:
- Describe the evidence used to recreate the past tectonic environments in California.
- Describe the tectonic setting of the Precambrian, Paleozoic, Mesozoic, and Cenozoic stages of development of California geology.
- Identify modern tectonic settings that we can use as analogs to understand the processes that created the geology of California.
- 6.1: Developing a Geologic History
- This page discusses how geologists study tectonic plates' distribution and movement, employing magnetic anomalies and fracture zones. By analyzing rock types—sedimentary, igneous, and metamorphic—and determining their ages, they establish a sequential geologic history. Continuous tectonic activity can hinder this process, necessitating diverse techniques for reconstructing and interpreting past geologic environments.
- 6.2: Precambrian California (4.6 Ga – 541 Ma)
- This page discusses the Proterozoic Eon, highlighting the supercontinent Rodinia's fragmentation and its impact on California's geological landscape. It notes California's role as a passive margin during this time, with limited tectonic activity leading to sedimentary rock accumulation. The rifting of Rodinia formed sedimentary basins and marine incursions, resulting in thick Precambrian marine sediments, which are now only partially visible in California, especially in the southeast.
- 6.3: Paleozoic California (541 – 252 Ma)
- This page details California's Paleozoic history, starting with passive margin sedimentation and shifting to an active margin during the Devonian with the Antler Orogeny, leading to compression and thrust sheet formation. The subsequent Sonoma Orogeny introduced the Golconda allochthon, highlighting further compression and subduction. The Paleozoic coastline is believed to be truncated due to the California-Coahuila transform fault, which disturbed the miogeoclinal margin sediments.
- 6.4: Mesozoic California (250 – 66 Ma)- Subduction and Mountain Building
- This page discusses geological developments in California during the Mesozoic era, highlighting the formation of the Sierra Nevada and Coast Ranges through subduction-related processes. Key mountain-building events, including the Nevadan, Sevier, and Laramide orogenies, shaped the region's complex geology.
- 6.5: Cenozoic California (66 Ma – Present)- Faulting, Uplift, and Basin Formation
- This page discusses the geological transformations in California during the Cenozoic Era, including the transition from subduction to transform boundaries that formed the San Andreas Fault. It describes the impact of tectonic changes on the landscape, the active Cascadia Subduction Zone producing the Cascade Range, and glacial events of the Quaternary period, which shaped the region's topography and coastline.
- 6.6: Chapter Summary
- A summary of A Brief Geologic History of California.
- 6.7: Detailed Figure Descriptions
- Descriptions of complex images within this chapter, as well as additional guidance for users who may have difficulty perceiving images.
References
- Cohen, K.M., Harper, D.A.T., Gibbard, P.L. 2024. ICS International Chronostratigraphic Chart 2023/09. International Commission on Stratigraphy, IUGS. www.stratigraphy.org (visited: 2024/10/18)
- California's Amazing Geology, 2nd, by Donald Prothero, 1032294906.
- Roadside Geology of Northern California, by David Alt and Donald Hyndman, 0878426701.
- Roadside Geology of Southern California, by Arthur Sylvester and Elizabeth Gans, 0878426531.
Thumbnail: "Northeast Pacific and Western North American Plate Tectonic History, animation" by Tanya Atwater is licensed under CC-BY-NC 4.0.