Welcome to Crestview Park, where a remarkable geological feature awaits your discovery! This EarthCache will guide you to a prominent outcrop that tells a fascinating story of ancient oceans, seafloor landslides, and the powerful forces that shaped the landscape of Aliso Viejo.
This outcrop is a beautiful exposure of the Monterey Formation, a vast and significant geological unit found throughout California. This formation is famous for its unique rock types and the role it plays in the state's oil and gas production. However, here, we will focus on the depositional environment and the clues left behind in the rock itself.
The Miocene Ocean Basin:
The Monterey Formation was deposited during the Miocene Epoch, approximately 6 to 23 million years ago. At that time, much of what is now coastal California, including Aliso Viejo, was submerged beneath a deep, nutrient-rich ocean basin. This basin was an ideal environment for the proliferation of diatoms, a type of microscopic, single-celled algae. Diatoms secrete intricate, protective shells made of silica (hydrated silicon dioxide, the main component of glass).
When these diatoms died, their tiny silica skeletons, called frustules, rained down to the seafloor, accumulating into thick layers of what is now known as diatomite. This light-colored, porous rock is the primary component of the layered sections you will see in the outcrop. Diatomite is known for being extremely light and low-density, a characteristic you can observe in many samples of the Monterey Formation.
Deep-Water Landslides:
While much of the diatomite was deposited in calm, deep-water conditions, the geology here shows evidence of more dramatic events. The continental slope in this area was steep and tectonically active. From time to time, seismic activity (earthquakes) or gravitational instability would trigger massive underwater landslides. These landslides, known as slumps, involved large blocks of already-deposited diatomite sliding down the seafloor slope. The moving mass often picked up and incorporated other types of sediment, such as deeper-basin muds, creating a jumbled, chaotic mixture.
The outcrop at Crestview Park is a perfect example of this process. You will see both the finely layered diatomite, representing calm, continuous deposition, and a more chaotic, disturbed section, which is a classic example of a submarine slump deposit. This outcrop is a literal snapshot in time, showing us the quiet, steady accumulation of life and the powerful, sudden forces of nature that periodically interrupted it.
To Claim This EarthCache, You Must Answer the Following Questions:
To log this EarthCache, please send your answers to the questions above to me via the Geocaching message system or email. Please do not post the answers in your log. You may log your find immediately after sending the answers. I will contact you if there are any issues.
1. Cache Identification: On the first line of your text, include "Outcropping at Crestview Park, GCBBBET."
Question 2: The Layered Rock
Observe the light-colored, layered rock (diatomite).
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a) Are the layers mostly straight and even, or are they bent and broken?
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b) Look at the layers where they are straight. Do they seem to be thick or thin?
Question 3: The Slump Deposit
Now, find the darker, more chaotic section of the outcrop.
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a) What do you see in this rock that makes it look different from the layered rock? (Hint: Does it have layers, or does it look jumbled and mixed up?)
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b) The contact between the two types of rock (the layered diatomite and the slump deposit) is visible in several places. Based on what you see, which rock was put down first, and which one came on top of it?
Question 4: Photo Evidence
At the posted coordinates, go up to the outcrop and take a photo with the outcrop in the background. If you are camera shy you may place a item you have with you in the photo. Please try not to give away any answers.
Cited Works:
https://www.usgs.gov/publications/monterey-formation-california-and-origin-its-siliceous-rocks
https://www.conservation.ca.gov/cgs/rgm/preliminary
https://ivc.edu/dept/geology/ocgeo