Geology of Cabrillo National Monument
Geological History
Formation and Uplift:
- Late Cretaceous Period: Approximately 76 million years ago, the rocks of the Point Loma peninsula were formed from sand, mud, and gravel deposited into the Pacific Ocean. This period marks the initial accumulation of these sedimentary layers.
- Quaternary Period: Over the last 2 million years, these sedimentary rocks were uplifted, faulted, and eroded, shaping the peninsula we see today.
Sedimentary Layers:
- Submarine Fan: Nearly 80 million years ago, sediments flowed from the eastern foothills and mountains into the Pacific Ocean, forming a large submarine fan composed of mud, sand, and gravel.
- Layering Disruption: Faulting interrupted the consistent sedimentary layering, causing an abrupt shift evidenced by a layer of sand over the top gravel layer.
Uplift Mechanism:
- Rose Canyon Fault: Compression along this fault caused the Cretaceous sediments to rise and tilt northeast at a 5-15 degree angle. This tectonic activity continues today, contributing to the ongoing geological evolution of the region.
Quaternary Period
Pleistocene to Holocene:
- The Quaternary period spans the last 2.67 million years, from the Ice Age (Pleistocene) to the present day (Holocene).
- Preservation: Due to minimal deformation during this period, much of San Diego’s Quaternary history is well-preserved. However, localized uplift has removed some deposits in the Point Loma area.
Quaternary Deposits:
- Marine Terrace Alluvium: Water-deposited sediments.
- Aeolian Sand: Windblown deposits.
- Colluvium: Gravity-deposited materials.
Further Reading
For more detailed information on the local geology, consider the following resources:
- “Understanding the Life of Point Loma” by the Cabrillo National Monument Foundation.
- “The Rise and Fall of San Diego” by Pat Abbott.
Visual Guides
Geology of Point Loma:
- This map illustrates the geologic layers at Cabrillo, offering a detailed look into the peninsula's geological composition.
Cabrillo Geology Field Guide:
- A comprehensive field guide is available for those interested in exploring the geological features of Cabrillo National Monument in greater detail.
