MARINE TERRACES AND THEIR BLUFFS

One of the most unique features of California's geology is the marine terraces that line its western coast. The most extensive terraces occur right here in Southern California, with Palos Verdes and Santa Monica rivaling in sheer magnificence.

Southern California terraces are among the oldest and highest. They are one to two million years old, part of the same uplifting process that formed the Coast Ranges. Even to this day they are slowly, incrementally rising. There are even younger terraces out under the ocean thrusting upward.

Such upward lifting of a land mass normally occurs along fault zones. There are three noted fault zones near Palisades Park.

See Faults below.

TELL TALE SIGNS IN A PROFILE

Terrace soils are generally thin, commonly composed of rock debris, marine fossil fragments, and shells which were all deposited when the terrace was still submerged beneath the sea.

As marine terraces rise from below the sea they face a new tide of terrestrial deposits,  thick alluvial deposits of sand and gravel from streams and rivers. 

Information from the California Coastal Resource Guide, 1987, California Coastal Commission

LAYERS: A MILLION YEARS IN ONE LOOK

You can see signs of alternating layers, each representing centuries, in the face of the bluff.   The layers show the interplay of marine deposits (rock debris, marine fossil fragments, and shells) and terrestrial deposits (thick alluvial deposits of sand and gravel from streams and rivers) in the formation of the bluffs. 

Information from the California Coastal Resource Guide, 1987, California Coastal Commission

 THIS LAND IS NOT STABLE AND WINTER IS A TRYING TIME 

"Because bluffs are composed mainly of sedimentary rocks such as sandstones and shales they are particularly prone to erosion.

Grains of quartz, feldspur, and mica compressed into layers of sandstone crumble easily.

When wet, shales and sandstone disintegrate, and clays and muds soften and liquefy."

California Coastal Resource Guide, 1987, p 18, California Coastal Commission

Heroic Effort

This heroic tree clings precariously to an eroding park bluff, all the while strenuously fulfilling its role in preserving the bluffs.

Notice the extensive lateral root development. That's an achiever. 

When water runs off the park's compacted soils or down artificial park drains, it will not be able to percolate into the soil to sustain this tree's roots. 

And the bluffs lose another heroic fighter for its sustainability.

 PIPES VS VEGETATION

 In Palisades Park there is a system of drains and pipes to divert water runoff especially during heavy rainfall. Heavily saturated soils weigh more and create pressure toward movement. Artificial drains are thus designed to divert rainwater away from slide areas.

Over reliance on artificial drainage, however, has created numerous problems. Drains can burst and wash out whole sections of the park.

According to USC Professor Samuel Goldberg, "Actions that funnel and increase water movement activate landslide triggers. For instance, water lines that break or leak and runoff channels that force water into specific locations pose glaring dangers."*

In the photo of a Palisades Park bluff we might conjecture:

(1) the drainage pipes were in part responsible for the erosion around them.

(2) the natural vegetation at left of the drain pipes is doing a better job in protecting the bluffs. 

 *Samuel Goldberg "Falling into the Pacific: California Landslides and Landuse." 

You may have noticed that eucalyptus is one of the main tree species in Palisades Park.

During the time the Park was being developed, from 1907 to 1913, was also one of the two most frenzied periods of planting this Australian transplant in California.

"At the time planters believed variously that eucalyptus would provide fuel, improve the weather, boost farm productivity, defeat malaria, preserve watersheds, and thwart a looming timber famine. First and foremost, however, Californians planted the trees to domesticate and beautify the landscape, to make it more green."*

Decades later we learn these trees not only make the land more green and beautiful; they also serve a vital mechanism by penetrating their roots deep into the bluffs and aggressively absorbing rainwater. This preserves and protects the bluffs. Often orchard owners will complain that the tree is a water hog or an invasive water sucker.  

At Palisades Park this unique thirst is a benefit. Rainwater percolates into the soil which encourages root development as the thirsty eucalyptus pursues its love of water. The extensive root development, penetrating rocky porous soils, binds particles together maintaining a stronger bluff that can withstand erosion.

*From "Gone Native: California’s Love-hate Relationship with Eucalyptus Trees"  by Jared Farmer