Geology
Sunset Cliffs Geology
Linear Section Geology
Both Ancient and Fragile…
The ancient Cretaceous Era bedrock of Point Loma, the Point Loma Formation, is considered to be 75 to 70 million years old. It stands in contrast to the much younger (less than 120,000 years old) Bay Point Formation sitting on top.
The resistant formation extends offshore where it forms the sea floor for several miles… creating platforms and reefs that actually slow down wave action on the cliffs… acting as a buffer.
The fragile Bay Point Formation is a porous sandy geologic layer that covered portions of the older Point Loma Formation when the peninsula was an island and formed when the sea level was higher 120,000 years ago. It is particularly vulnerable to erosion. (Planting native plants with their deep roots helps hold the soil.)
Sources of erosion besides wave action include foot traffic, excessive irrigation, and storm water runoff. Understanding the processes of erosion at the cliffs helps us anticipate change and appreciate the dynamic sculpting process of our unique cliffs.
(Building seawalls hides the dynamic processes at work. Riprap is known to accelerate the natural processes of erosion by grinding away the Point Loma Formation at the base of the cliffs. Both detract from the beauty of the cliffs.)
Dynamic Sculpting Processes at Work
Caves, sinkholes, arches, sea stacks, and sand are visible indications of nature at work.
Waves splashing against the cliff face and carry water into cracks such as faults in the ancient and sturdy Point Loma Formation, enlarging the cracks and contributing to the sculpting process. Water draining through the upper cliff Bay Point Formation into the lower Point Loma Formation also contributes to the sculpting process.
Sea caves may form and enlarge over time….demonstrating the strength of the ancient sedimentary Point Loma Formation.
When the “ceiling” of a sea cave collapses, a sinkhole appears. Over time, arches are left connecting walls of the former cave. Over time the sea cliff “retreats” landward, leaving sea stacks as the final visible remnants of sea caves. Eroded cliff formations become sand for coves and beaches along the coast.
Good Tide Pooling Etiquette
Protect me. Please don’t touch me or pick me up.
Please don’t remove me from my home!
Please don’t litter. This is my home. Would you like to live in a trashy tide pool?
Watch out! The tides are always changing. Never turn your back on the incoming waves.
My home is slippery. Be cautious when climbing on rocks.
Why should we care?
There has been a decrease in the average size of many organisms through the years due to the harvesting of larger individuals for human consumption. This is especially problematic for hermaphroditic species like Owl Limpets, whose larger and older individuals transition from male to female. Thus, harvesting leads to distorted sex ratios and decreased reproductive rates [Condensed for sign: Harvesting for human consumption has led to a decrease in average size of hermaphrodite species like Owl Limpet, resulting in distorted sex ratios and decreased reproductive rates.} (Kaustuve 2007 (1)), Sagarin et al., 2007 (2), 3)
Human trampling leads to significant and lasting declines in density and diversity, especially of leaf-like algae, barnacles, and mussel beds. (Newman 2008 (4); Addessi 1994 (5))
Black abalone, once an abundant inhabitant of southern Californian intertidal regions, has suffered severe population declines, leading to the closure of commercial and recreational fisheries in 1993 and classification as endangered since 2009. Overfishing, low densities resulting in low reproductive rates, oil spills, and a fatal disease called withering syndrome that is accelerated by warming ocean waters have led to the decline. The populations began to slowly rise in the 2000s, but illegal harvesting is still a threat to their recovery (NOAA Fisheries (6); Raimondi et al, 2002 (7)).
Related Websites and Books
The Cabrillo National Monument has in-depth information about the history and geology of Sunset Cliffs and Point Loma as a whole!
Cabrillo National Monument Foundation: "Understanding the Life of Point Loma" - Chapter 1: From Sea to Shore: Biologic History