Bayside Journey to the Cretaceous EarthCache
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Bayside Journey to the Cretaceous
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The Bayside Trail at Cabrillo National Monument is a 2-mile hike along the eastern side of the Point Loma peninsula. It overlooks San Diego Bay, Coronado, Downtown San Diego, and the Naval bases. Here you have the special opportunity to explore the unique coastal sage scrub habitat that is native to this region of San Diego. You will also have the opportunity to view some U.S. historical sites from World War II.
Cabrillo National Monument is open 364 days a year, from 9:00 AM to 5:00 PM - we are closed Christmas Day, December 25. The Bayside Trail closes at 4:00 PM and all visitors must exit the park by 5:00 PM.
The hike along the Bayside Trail gives you some of the most breathtaking views in all of San Diego, but it also allows you to get up close to some of the geologic features that helped form the peninsula over 65 million years ago! Erosion from the Peninsular Ranges east of Point Loma are responsible for the peninsula’s existence today. Several million years of eroded material washed into the Pacific Ocean and was collected in a submarine fan consisting of two main components, the inner-fan valley, and the mid-fan channel.
The inner-fan valley consists mostly of the small to large gravel deposits located fairly close to the shore. The mid-fan channel consisted of the fine sands that were able to flow out further from the coast because they were much lighter than the heavy gravel, which could reach the size of a microwave or even larger. As the fan was growing westward, mud layers were covered by sand layers, which were eventually covered by gravel layers.
However, due to faulting and sea level change, sand began to be deposited once again, now on top of the gravel layers. The Rose Canyon fault, which is responsible for the change in sea level and sediment deposition, is also responsible for the uplifting force called “compression” that brought the deposited material from 2/3 of a mile below the sea floor up to the surface. These upper sand layers created the sandstone cliffs that are exposed along the Bayside Trail.
Here you will have an opportunity to see the exposed sandstone cliffs (32° 40’ 15.38’’ N, 117° 14’ 17.81’’ W) that are millions of years old, as well as some of the conglomerate layers created by the gravel. Enjoy the beautiful view and the history that surrounds you and remember to stay on the designated trail.
1. Name of the cache and how many people were in your group.
2. About how thick is the conglomerate layer? Where do you think this material originated?
3. Thanks to the local faults, portions of the marine sediment were uplifted forming an island. What event occurred roughly 10,000 years ago that connected the mainland to this island, forming the peninsula?
4. How long ago were the sandstone beds that created the peninsula deposited?
5. Describe the coloration of layers within the exposed sandstone (32° 40’ 15.38’’ N, 117° 14’ 17.81’’ W).
Additional Hints
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