Have you ever considered the composition of our local mountains, hills, and cliffs in Orange County? To explore these amazing abiotic or nonliving features, we must delve into geology to understand how certain rocks are formed, their structures, composition, and types of processes acting on them. Rocks provide evidence of past environments, geological processes, and life forms through their composition, texture, layering, and the fossils they contain (Holtz, 2022). Orange County has a long history that can be told by just rocks. Under us, and in places such as bluffs and cliffs, is a formation of rocks called the Monterey Formation. It is a sedimentary rock formation visible throughout Orange County, particularly at Upper Newport Bay and Crystal Cove State Park, formed 25 million years ago during the Miocene period. Sedimentary rock is made up of sediment, solid material that is moved and deposited in a new location. This can be composed of other rocks, minerals, plant and animal remains, sand, mud, pebbles, and fossils. Crystal Cove State Park has geologic features such as folds, magnetite, fossils, and many more, which will be reviewed below.
Along Crystal Cove State Park and Beach, you'll find a variety of fascinating geological features that you might not have noticed. Some rocks have 120,000-year-old fossils within one big formation similar to a conglomerate rock, which is made up of eroded rock fragments and pebbles cemented with fine grains of sand, silt, or clay. Instead of rocks on rocks, it is fossils. This is caused by the organisms getting buried by sediment like mud or sand. Then, over time, more sediment is deposited on top of the buried organism, putting pressure on the layers below. After all that, the layers of sediment harden into sedimentary rock. These rocks actually originate 3/4 of the way up the cliff. These rocks are in a bed that lies immediately above the Monterey Formation. In geology, a bed is a sediment layer separated from other layers. The Monterey Formation is about 6 million years old, so there is a time gap between the fossils and the formation, and this is what geologists call an unconformity. This unconformity appears as an overhanging fossil bed “shelf.”
Left: The top is a rock with shell pieces embedded within it, and the bottom one is a conglomerate with pebbles and stones rounded in an aquatic environment and cemented together by a fine-grained matrix of silt and clay. PC: Alondra
Right: The second picture is a fossil bed “shelf” where the rocks come from. PC: Crystal Cove State Park
Crystal Cove also has columnar jointing in volcanic rock made of andesite. This fine-grained igneous rock cooled from lava at or near the Earth’s surface creates a pattern of intersecting fractures that form columns. The original magma contracted while it cooled, creating this repeating jointing pattern. This is evidence of volcanic activity in Crystal Cove, showing igneous rocks formed from molten magma uplifted from beneath the subduction zone just offshore, part of the ‘Ring of Fire’ that rings the Pacific Ocean.
Columnar jointing in Crystal Cove Beach Left PC: Poopy Archaeology / Youtube; Right PC: Geologically Speaking / Youtube
Crystal Cove, which is in the Monterey Formation, also has extreme anticlines and synclines and folds in rocks, so much so that the rocks look like folded taffy in places along the cliffs. Anticlines are upward folds that form hills, and usually, the oldest rocks are pushed up in the middle, and each half of the fold dips away from the crest. Synclines, however, have upward folds that usually form valleys, the youngest rocks are pushed down in the middle, and each half of the fold dips towards the trough. This is usually caused by the extreme compressional stress within plate boundaries, causing the rocks to move either upwards (to form an anticline) or downwards (synclines, creating an arch). There are also recumbent folds with an axial (center of the fold) plane that is almost horizontal so that the limbs of the fold are nearly parallel to each other.
See the figure below:
Moving inland, if you're hiking around the Upper Newport Bay or helping us restore it, you will notice the white cliffs of Upper Newport Bay because they contain microscopic diatoms from the Monterey Formation (OC Parks). Diatoms are microscopic algae, and they are important to the Monterey Formation because their accumulated remains, known as diatomite, make up a significant portion of the formation, acting as the primary source of organic material that eventually turns into oil deposits. In addition, diatoms can be used to determine the age of sediment because they sink to the ocean floor when they die. Overall, the Monterey Formation is composed of compressed diatom shells (Freya, 2016). A little history about the area is that nearly 9,000 years ago the Gabrielinos lived there. In 1934, the area became The Salt Works by the Irvine Company. Over 500 tons of salt was produced per season and it was used to produce water softener salt. The Salt Works closed as a result of extensive damage caused by the flood of 1968-69 and remnants of the work can be seen still within the area. Irvine Company was going to develop the “Swamplands” into a bustling boat and locale until a kid known as Jay Robinson went into the area and was kicked off the property and his parents were upset. The parents started a petition called “Save the Bay” which got lots of resident signatures to support. As a result of their collective efforts, in 1975 the Upper Bay became an Ecological Reserve managed by the California Department of Fish and Game.
Figure 1: Upper Newport Bay; Figures 2 and 3 are a closer look at the white diatoms. PC: Alondra Ruiz
Moving even more inland in Orange County to explore other geologic features, there is Black Star Canyon Wilderness Park in Silverado. During the Cenozoic Era, about 20-40 million years ago, the sedimentary rock formation called Red Rock formed (Irvine Ranch Conservancy, 2020). The Red Rocks developed their famous red color and jagged appearance over time due to oxidation (or rust) of the sediment and erosion. The metals that oxidize are iron, copper, manganese, lead, and zinc. This happens when exposed to oxygen and water, which form an oxide mineral called hematite (iron oxide), which makes the rocks red.
Next time you hike or walk around these locations, you may have a greater appreciation for these features and how they came to be. OC Habitats regularly leads educational and restoration events in Orange County since one of our organization's pillars is educating the public, including our volunteers, about our natural habitats, species, environmental impacts, and more. At some of these events, you can glimpse the formations discussed in this article, such as our UNB restorations mentioned above or when we have our Marine Protected Area (MPA) hikes.
Sources:
Crystal Cove State Park. (2009). Geology discovery trail. Geology Discovery Trail. https://www.crystalcovestatepark.org/wp-content/uploads/2016/10/GeologyGuide112309small.pdf
Crystal Cove State Park. (2018, December). Geologic Points of Interest. Coast Guide. http://www.crystalcovestatepark.org/wp-content/uploads/2018/12/Crystal-Cove-Geology-Coast-Guide-optimized-print.pdf
Editor, I. R. C. (2020, November 20). Landmarks focus: Black star canyon wilderness park. https://www.irconservancy.org/landmarks-focus-black-star-canyon-wilderness-park-html/
Holtz, T. (2022, November 14). Reading the Rocks: How the Earth and Life through Time Document Global Change. CPSG 100 Science & Global Change: Reading the rocks: How the earth and life through time document global change. https://www.geol.umd.edu/sgc/lectures/elt.html
Mitchison, F. (2016, August 15). So, What Exactly Is A Diatom Paleontologist...?. Joidesresolution.org. https://joidesresolution.org/so-what-exactly-is-a-diatom-paleontologist/
OC Parks. (n.d.). History. https://www.ocparks.com/parks-trails/upper-newport-bay-nature-preserve/history
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