Crystal Cove State Park Beach Geology

Thank you for downloading the Crystal Cove Geology Guide by Dr. Merton Hill brought to you by Crystal Cove Alliance, the non-profit co-operating association for Crystal Cove State Park.

This Geologic Points of Interest guide takes you to the shore where the (locally) 12- to 6-million-year-old rocks of the Monterey Formation crop out.

The ocean environment, marine life and sediments combine to produce fossils,concretions and one of California’s richest petroleum source rocks – the Monterey Formation.

Beginning 25 million years ago sediments (sand, silt, clay, and organism skeletons) slowly accumulated in shallow Pacific Ocean waters and formed the geologic layer known as the Vaqueros Formation, the oldest exposed rock unit in the park.

Our first Point of Interest (POI) is along the south side of the Los Trancos parking lot. Observe the cracks in the sidewalk and adjoining asphalt pathway. Why are
they here?

Ground movement is the answer. But what kind? Faulting, clay soil expansion and contraction, mass wasting (the
downward movement of rocks or soil due to gravity – ranging from high speeds such as rock fall to very slow creep), or some other movement? All are possible and occur in the park. Here, expansive clay soils and soil creep are most likely (although large faults – the Newport-Inglewood, Pelican Hills, and Shady Canyon – occur in and near the park). Cracks nearly paralleling streets as in the picture below, indicate creep is a likely culprit.

Why does the water run year round even long after the rainy season? Why does it commonly flood the tunnel under Pacific Coast Highway just ahead?

The answer is urban runoff. This is water from
homeowners’ landscape, city streets, and the golf course. Despite the constant flow, runoff is now much reduced since the installation in 2007 of an elaborate water capture and storage system. The steel doors in the pavement (photo below) hide the system’s water pumps.

Just before the tunnel you will see hard crystalline boulders embedded in the concrete. These igneous rocks (formed from molten magma) are not natural to the park but were imported to minimize erosion.

Nonetheless, look closely at their grain size and color. On this side of the tunnel, most are coarse grained (you can see individual crystals with your naked eyes) and dark in color due to iron and magnesium. When magma cools
slowly within Earth’s crust, the crystals have time to grow and produce coarse grained texture. Such rocks are called plutonic, named after the Greek god Pluto, ruler of the under-world.

At some places in the sand you will see streaks of fine black particles. Without really analyzing it, some people conclude these are crude oil or tar. However, if you run a magnet through the streaks, the particles will stick.

The black needles are the mineral magnetite, a component of ocean floor basaltic (volcanic) igneous rock. These needles have a positive and negative pole and orient to the magnetic field in which they are placed (in this case, in the field of the magnet).

Unlike mountain streams which run quickly and fairly straight and produce V-shaped canyons, streams in areas of low gradient (slope) run slowly and meander (make snake-like curves in their beds) and produce wide flat flood plains. Here you see a scale model of the latter. The outside walls of the bends are called cut banks. As time goes by the stream laterally cuts into this bank and carries away the eroded sand. In contrast, sand is deposited on the inside of the bends called point bars. Erosion occurs where the stream runs more quickly (the outside of bends) whereas deposition occurs where the stream runs more slowly (the inside of bends). Look carefully and you may witness the sideways movement of the entire stream bed. Over time, meandering rivers move sideways through the landscape just like some
snakes move sideways over sand dunes.

Notice also the ripples in the stream bed. These are small migrating sand dunes. Sand on the upstream side of the dunes erodes away whereas the same sand is deposited on the downstream side of each dune. The result is that through time the ripples march downstream. If you are here on a windy day, you may observe dry beach sand in the form of tiny dunes migrating down wind in much the same way the water ripples migrate downstream.

So in this one spot you’ve witnessed migration of two types – sideways in the stream bed and downstream in the dunes.

Walking south you see the last historic cottage. The “Beaches Cottage” was featured in a 1988 film starring Bette Midler, Barbara Hershey and John Heard. Despite its fame and photogenic character, it was one of the last Crystal Cove cottages to be restored. Why? Because mass wasting of an unstable cliff of Monterey Formation in its back and side yards threatened its destruction until a retaining wall was built.

The Monterey threatens landslides and slumps wherever it crops out in cliffs from San Onofre northward through Crystal Cove, Newport Back Bay, Santa Barbara, Lompoc, Santa Cruz, and Monterey. Mass wasting has taken down houses, roads and even people along with the rocks. Geologists know to be especially wary when building structures on or down slope of this unstable formation.

In the Beaches Cottage photos, you can see the dramatic difference in sand height at different times. Beach frequenters may know that sand height varies with wave size, length and direction. Visitors may not realize that along our shores over 200,000 cubic meters of sand are moved each year by the longshore (wave-generated) current. If nourishment sands were not added along our coast, we’d lose our sand permanently to the offshore submarine canyons where the current dumps it.

Visitors to Crystal Cove often ask about the hamburger bun-shaped or UFO shaped rock “formations” littering the
beach especially in the vicinity of the Beaches Cottage. These features range in size from a few inches to more than 12 feet in diameter. Look carefully in the cliff
towering over the side yard of the cottage.

You will see several examples embedded in the Monterey. Geologists call these bodies concretions. Although
small examples are common, large specimens like many here are relatively rare - although do occur elsewhere in
California such as along the Santa Barbara Coastal Plain and at Bowling Ball Beach at Schooner Gulch near Point
Arena.

Concretion formation is a fascinating story. A favorite hypothesis is that the rounded masses are like tumors growing in the body of an organism. If you are
unfortunate enough to get a splinter under your skin, your body reacts. The site may become infected by bacteria or other microorganisms, and a “tumor” forms
walling off the splinter from healthy tissue.

The Monterey also grew “tumors” by being infected. How? The Monterey formed in a mile plus deep marine environment. Clay and other fine-grained sediment such as diatom and calcareous plankton tests (skeletons) accumulated to form an ooze (a marine sediment with more than 30% organic material). Heavy rain and flooding brought wood to the beaches. Some drifted out to sea, became water-logged, and sank into the ooze.

These “splinters” became infected with bacteria which interacted with the sediment and the wood to produce swelling. The ooze with the nodules ultimately turned to stone.

Walk further south and you will see these shells embedded in sandstone on the beach adjacent to the cliffs. You may not give them a second thought. Although to the casual observer they appear modern, they are about 120,000 years old. This seems a great age to humans, who typically consider time in hours, days, weeks, years, and human lifetimes. To geologists 120,000 years is just a blink of an eye in a world exceeding 4.5 billion years in age. Because 120,000 years is so little geologic time, these fossils look like modern shells.

At the southern-most point of Crystal Cove you will find cliffs of andesite (a fine-grained igneous rock which cooled from lava at or near Earth’s surface). Geologists term this kind of rock volcanic as opposed to coarse-grained plutonic rock which cooled deep in Earth’s crust.

Here the lava cooled quickly and produced well-defined prismatic columns. Two world famous locations visited by tourists for these columnar joints are Devils Post Pile near Mammoth Mountain, California, and the Giant’s Causeway in Northern Ireland.

The severely folded Monterey beds exposed in the cliff at the north end of the beach at Crystal Cove are textbook examples of recumbent folds. These layers are so tightly contorted that it is hard to imagine solid rock bending like this – even under high heat and pressure. Despite the extreme folding, no visible faults are associated with this outcrop. Consequently, these rocks likely folded, not deep within Earth’s crust, but at the surface before the sediments lithified (turned to stone).

Picture yourself pushing a carpet up against a wall until it folds. Similarly, in the deep water environment, the water-saturated sediments probably slid (triggered by an earthquake) down slope until they folded as you see here.

You may have already noticed black oily patches on some of the rocks or the beach sand. Be careful with your
identification. Some of the spots may actually be “tar spot algae” or magnetite. On the other hand, some may indeed be petroleum.

On a clear day you can see oil platforms off shore Newport and Huntington Beaches. These platforms may host
several dozen wells radiating like spokes from the hub of a wheel and extending down to various reservoir rocks (porous, permeable rocks capable of yielding oil
and gas). One thing these platforms and many other land-based California oil wells have in common is that the source of oil is the Monterey Formation (although it has since migrated to various reservoir rocks).

Nearly all oil originates from plankton in shallow marine environments – not from land plants, which when preserved as fossil fuel produce coal.

From the beach climb the steps up to the bluff top and follow the path left to the Newport Jetty overlook. When looking north toward Corona del Mar, you will see
the Monterey cropping out all along the beach. Now observe the rocks exposed on the inland side of the trail. They appear very similar to Monterey Formation rocks rising out of the beach sand and making up the cliffs of the cave and surrounding areas. But we are standing on the 120,000-year-old soils and elevated
terrace deposits which overlie the Monterey cliffs. What is the problem? How can Monterey Formation be both above and below the terrace deposits?

Look at the Monterey exposed above the trail very carefully. You may have figured out the solution. The rocks above the trail are fake, bogus, manmade! They cover a retaining wall meant to look like the rocks in the vicinity.

Thank you for taking the Crystal Cove State Park Geology Tour. We hope you have gained some knowledge and had fun in the process! This guide was written by Dr. Merton Hill, Saddleback College. Editing & images provided by Dr. Annlia Hill, UC Irvine with the assistance of Crystal Cove State Park personnel, and brought to you by Crystal Cove Alliance.

Please remember to protect your park. Enjoy only trails designated by park maps and signs, For camping, reservations are required. Be prepared. Pack plenty of water, snacks, sun screen, and other backcountry essentials & enjoy this beautiful park.