Welcome to Coronado
Along 5th Street in Coronado, California, a subtle geological feature lies hidden in plain sight — a fault scarp formed by movement along an active fault zone. This EarthCache invites you to explore the fascinating world of fault scarps, learning how they form and what they reveal about the tectonic forces shaping Southern California.
The Formation of Fault Scarps
Fault scarps are landforms that form when the Earth's crust shifts along a fracture known as a fault. These features typically appear after an earthquake, when movement along the fault causes one side of the ground to be raised or lowered relative to the other. This vertical displacement creates a noticeable step or slope on the surface, known as a fault scarp. The height of a scarp depends on how much the ground has moved, what kind of fault is involved, and how many past earthquakes have occurred in the area. Some scarps are only a few inches tall, while others can reach several feet or more.
Scarps can form along different types of faults. Dip-slip faults, which include normal faults and reverse faults, produce mostly vertical motion and often create prominent scarps. Strike-slip faults mostly move sideways, but if there is even a small amount of vertical movement, they can also produce scarps. This type of motion is called oblique slip. Over time, repeated movement along a fault can cause a scarp to grow taller and more noticeable, especially in tectonically active regions.
In Coronado, the scarp you are seeing formed along a branch of the Rose Canyon Fault Zone. This fault system runs through the San Diego region and is considered active. The Rose Canyon Fault is mainly a strike-slip fault, which means the ground moves horizontally, but it also has a small vertical component. That slight vertical movement has added up over time, resulting in the low fault scarp that is visible today.
Geological Significance
The Coronado fault scarp is part of the Rose Canyon Fault Zone, which runs through San Diego County and extends offshore. This fault is capable of producing moderate to strong earthquakes. The Coronado strand of the fault follows a northwest to southeast path and can be traced in surface features like the scarp at this location. Studying fault scarps allows geologists to better understand past earthquake activity, monitor ongoing tectonic movement, and assess seismic hazards in populated areas. Urban fault scarps like this one also highlight the importance of earthquake-safe infrastructure and city planning.
Why Is This Important?
Examining fault scarps offers insight into:
- Tectonic Processes – How fault movement shapes the Earth's surface.
- Earthquake History – Evidence of past seismic activity in a specific area.
- Seismic Hazard Awareness – Understanding where active faults lie in developed regions.
Tasks for This EarthCache
To log this EarthCache, visit the site and complete the following tasks. Send me your answers via Geocaching or email.
- Include "Fault Scarp - Coronado - GCB75EY" on the first line of your message.
- Stand at the intersection of 5th Street and A Avenue. Look down 5th Street in the southeast direction. Do you notice any change in slope or uneven pavement? Describe what you see that could indicate a fault scarp.
- Measure the elevation at the top and bottom of the slope where the scarp is most visible. What is the elevation difference in feet or meters?
- Walk along the slope to estimate how long the scarp runs from one end to the other. How far does it extend? Does it appear continuous or broken up?
- Based on your observations, what type of fault caused this scarp? Did it likely form before or after the road was constructed?
- In your log, attach a photo of yourself or a personal belonging with the 5th Street and A Avenue street signs in the background. (Note: photos predating the publication of this EarthCache are not accepted.)