Part 2 of this series on California's San Diego area explores baby seals and national monuments. It also features more world-class deep-water outcrops from a recent field trip with Applied Stratigraphix, led by rockstar Tim Demko! You can read Part 1 here or just jump right into Part 2! Let's go!
Molly Turko
Structural Geologist, Devon Energy
La Jolla and Cabrillo Geology
Wipeout Beach and Cabrillo area geology/Courtesy of Molly Turko
About 25 minutes northwest of San Diego proper, La Jolla is often where many tourists consider to be their favorite area near San Diego. With beautiful beaches and intriguing geology, what's not to like?
Thirty minutes south on the tip of Point Loma, the Cabrillo National Monument area offers similarly scenic coastal views.
Exposures along the coast in these areas feature primarily Eocene deep-marine deposits (roughly 50–65 Ma) from submarine fan and slope systems.
These systems shed westward into a forearc basin along the active continental margin.
Deposition occurred as the Farallon Plate subducted beneath North America, driving basin subsidence, sediment supply from an uplifting magmatic arc, and gravity-driven transport into deep water.
Later Neogene transtension from Pacific–North American plate reorganization uplifted and faulted these deposits, exposing them for rock nerds to enjoy!
What is a submarine fan and slope system?
In part one, we examined deep-water channel complexes. Now, we will focus on the sides and the frontal parts of deep submarine fan lobes.
Here, flows spread into lobes with sheet-like sands that show better lateral continuity than the amalgamated channels seen previously.
Pay attention to critter diversity, bed continuity, thickness, and clay content, while watching for cool syn-depositional deformation.
The rocks here display lobe and channel-lobe transition zone lithofacies and stacking patterns. Look for:
Greater lateral continuity and fewer erosional surfaces than the channel complexes at San Clemente
Higher clay content and greater critter diversity, signaling a calmer, more oxygenated environment than that in channels
Abundant soft-sediment deformation, including epic “ball and pillow” structures and pseudonodules
Large NE-SW-oriented fracture systems big enough to walk through
Trip tips:
Visit at low tide and use caution when swimming. Rip currents and waves can cause “wipeouts!”
Park at Children’s Pool to the north and enjoy the baby seals. It's cuteness overload 😍
Fun fact: The historic seawall, built in 1931–32 as a wave-free children’s play area, has been occupied since the 1990s by a large harbor seal colony for resting, molting, and pupping.
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The beach at Cabrillo National Monument/ Courtesy of Molly Turko
Established in 1913, Cabrillo National Monument commemorates Juan Rodríguez Cabrillo’s 1542 landing, the first European expedition on the U.S. West Coast. It includes the historic Old Point Loma Lighthouse, panoramic bay views, solid spots for whale watching, tide pools, and military bunkers.
Head down the trails to the beach and observe:
Medial-distal lobes facies with thinner beds and thicker muds, yet still a bit of sand
Reduced critter diversity, indicating less oxygen, as it was a bit muddier
Fracture spacing versus bed thickness relationships. Mechanical stratigraphy for the win!
Trip tips:
Exploring is best done at low tide, especially to see all the animals and plants in the tide pools!
Keep an eye out for ships and submarines from the nearby Naval Base Point Loma.
Go deeper: Check out drone footage from our trip here.
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