Santa Barbara Geology

The following is from Santa Barbara Day Hikes by Ray Ford

Man has permanently altered the character of the valley floor along the coast, but the wilderness of the mountain wall, the dense chaparral, and the rugged terrain have defied his desire to exploit it. It is a land that appears out of place in the modern world, seemingly unchanged and unchanging, its geological structure moving at an infinitesimal pace, evident only in the cataclysmic moments when the earth shudders. 

The bedrock of these mountains is the sand of time itself, and is always changing, quite independently of man. The layers of sandstone and shale exposed along the crest of the Santa Ynez Mountains, now thousands of feet above sea level, once lay several thousands of feet below the sea, and may yet lie there again, as the forces of erosion wear away at the resistant rock. 

The Transverse Ranges, of which the Santa Ynez Mountains form the most westerly part, is one of the few ranges in the United States that runs in an east-west direction. Forming a continuous crest from Point Arguello to Ojai, a distance of 70 miles, the Santa Ynez Mountains are tilted steeply to the south at an angle of nearly 50 degrees.  

From Point Arguello to Gaviota Pass, the range is generally less than 2,000 feet high. East of Gaviota, however, the mountains gain height rapidly, reaching 4298 feet at Santa Ynez Peak, before dropping gradually to San Marcos Pass which has an elevation of 2250 feet.

San Marcos Pass occupies a low saddle formed by a synclinal (V-shaped) fold that crosses the main axis of the range diagonally. East of San Marcos Pass, the mountains  rise once again, averaging 3,500 feet behind Santa Barbara, with La Cumbre Peak measuring 3985 feet in height. The range reaches its apex at 4,690 foot Divide Peak, near the Santa Barbara-Ventura county line.

The geologic history of the Santa Ynez Mountains is related to the slow movements of pieces of the Earth’s crust called tectonic plates. At present, Southern California marks the boundary between two of these plates, the North American Plate, which supports most of the continental United States, and the Pacific Plate, which supports a part of the California coast and Baja California. The point at which these two plates come into contact is called the San Andreas Fault. 

The movement of the plates is called continental drift.  The action of this “drift” can cause several things to happen at the point of articulation between two plates. They might be pulled apart, which creates a trench between them. Or one plate can be pushed over the other, a process called subduction.  Also, two plates can slide against one another, as presently occurs along the San Andreas Fault. Santa Barbara’s geologic his-tory involves all three of these processes.

Deep Time
One morning, standing in  Mission Creek near Rocky Nook Park and the Museum of Natural History, I gained a fleeting understanding of the awesome amount of time involved in the unfolding of the geologic processes that created the Santa Barbara landscape. Deep time. 

The creek flowed gently through rounded sandstone boulders and rocks, some of which had shells imbedded in them. I meandered through the rocks, enjoying their different colors and textures, wondering how far up the mountain wall they must have come from.

As I picked up a hand-sized rock, etched with small pock marks and wavy white lines that must have been clam shells at one time, I could see Mission Crags through the crown of an ancient oak, lofty rocks thrust high into the sky. I thought, “This rock must have been up there once; but now it is almost back home, back in the sea. Like the water flowing down the creek, the rock must also be part of a cycle.”

The water molecules in Mission Creek will flow quickly to the ocean, evaporate into the atmosphere and be moved by currents of air back to the mountains to be deposited as a misty fog or huge drops of rain then carried back down once again, a cycle that can be measured in weeks or months. Not so for this small piece of rock.

Once part of a marine bay filled with ocean life, possibly fifty million years ago, it was lifted slowly into the sky by monumental, earth-shaking forces, then exposed, crumbled and worn away by the erosive forces of wind and water, and finally pushed back down the mountain to this spot near Rocky Nook Park by a combination of water and gravity.  On another day—perhaps five thousand to ten thousand years from now—it will find its way back into the ocean, part of another marine layer awaiting its time to be thrust back into the sky.

A few days after my trip to Mission Creek, when I got the slides back from my trip, I found one taken at 1/250th of a second which showed the water flowing over the rocks, but captured in frozen motion because of the speed at which it was taken. The sheets of water looked very much like the rock, frozen in motion, and frozen in time, for all intents and purposes no more living or flowing than the bedrock which made up the backbone of the Santa Ynez Mountains.

I thought again, “What of a creature whose lifespan was but a 1/250th of a second in length, a creature which was born, lived and then died within this short period of time? What would it think of the water in Mission Creek? Would it die thinking that water was something like we think of rock?

In comparison to the one hundred and thirty-five million years that Santa Barbara’s geologic history has encompassed, the length of our own lives will last just about a 1/250th of a second. Like the small creature which only saw frozen water, when in fact it was a living, moving, vibrant substance, our view of the geologic processes is very limited and incomplete.

 When we begin to sense life on this larger scale, one which encompasses a hundred and thirty-five million years and the evolution of our present geology and chaparral plant communities, Santa Barbara’s environment  is no longer a static thing, but a living, breathing system, and we begin to be in tune with a deeper time. 

The Subduction Begins
One hundred and thirty-five million years ago, the North American and Pacific Plates came into contact with one another for the first time, initiating a series of violent collisions that would shape the geology of all of Southern California. There was a much different topographic relief then, dissimilar vegetation (in the areas above water), and a climate much wetter than what we know at present. 

There were no high mountains in California, perhaps only rolling hills, and a tropical sea lapped against a shoreline much farther east, near the base of what was to become the Sierra Nevada. What we now know as Santa Barbara was underwater and farther south, possibly as far south as northern Baja. 

Much of  northern California, however, and most of the Pacific Northwest was above water. Dense rainforests predominated in the Northwest and the climate was warm, temperate, and humid. In the parts of Southern California that were above sea level the climate was more subtropical and savanna, rolling grass-covered hills set in a warm, wet climate.  

But gradually this began to change as two massive pieces of the earth’s crust smashed together. While both the North American and Pacific Plates drifted northward, the Pacific Plate moved north at a faster rate, causing it to collide with the North American land mass. Though the difference in rate of drift was miniscule, an average of only 2.25inches per year (some 300 miles over the entire 135 million year period!), this difference was enough to produce Southern California’s rugged topography. 

The Pacific Plate was composed, not of a single sheet of the earth’s crust, but a series of connected pieces. In its  middle portion was a break known as the Pacific Rise, out of which oozed molten materials from deep within the earth. Like escalators, the land on each side moved up and out and away  from the Rise. 

Thus, as the Pacific Plate drifted north, there was also a part of it that moved to the east, causing the plate  to be pushed, or subducted, under the North American Plate at some periods in its geologic history, and at others to slide north against it, as it does today along the San Andreas Fault.

As one of the pieces of the Pacific Plate subducted under the continental piece, the edge of the North American continent acted like a huge bulldozer blade, scraping portions of the crust off the ocean plate. This pile of rubble, called the Franciscan Formation by geologists, eventually would become the basement rock beneath the Santa Ynez Mountains. Today, it is exposed in Santa Barbara County mainly along the southern slopes of the San Rafael Mountains, especially near Figueroa Mountain.

Farther to the interior, the subduction caused widespread volcanic activity in the Sierras, with friction between the two plates causing rock beneath the surface to melt and  the land directly above the western edge of the North American Plate to sink. As the basin subsided, it formed a large depression something like the shape of a bathtub. 

This bathtub began to fill very slowly with the sediments that would one day make up the Santa Barbara front and back country. Most of the geologic formations exposed in the Santa Ynez Mountains, including the Juncal, Matilija, Cozy Dell, and Coldwater formations, were deposited in this basin during the Eocene Epoch, 40 to 50 million years ago. 

As the basin continued to sink, the shoreline crept inland to the base of an ancestral form of the Sierra Nevada, which were more rolling hills than mountains at that time. While the Sierra range was uplifted, torrential subtropical rains caused widespread erosion, covering the ocean floor with 20,000 to 30,000 feet of sediment that would eventually become the fertile Central Valley and the Santa Barbara coast. 

  The sinking of the basin and the consequent sedimentation were not processes that occurred evenly, though. At some points as the basin sank rapidly the ocean was several thousand feet deep; at others, it subsided slowly or not at all, and the basin filled to become a shallow seashore environment.

When more shallow, a predominance of sands built up, like  those in prominent peaks such as La Cumbre or Divide Peaks, or massive pieces of bedrock such as those at Lizard’s Mouth or the Playground. Where the basin was deeper, the shales prevailed, shales like the Cozy Dell, which lies in between the Matilija and Coldwater sandstones and forms the deep saddles that make Mission Crags so distinctive.

 Finally, at the beginning of the Oligocene Epoch, approximately 35 million years ago,when the section of the Pacific Plate causing the basin to sink moved north of Southern California, Santa Barbara was about ready to surface for the first time. The basin, or bathtub, was  almost full of sediment and as the shoreline began to retreat westward, the land began to re-emerge.

At this point, Santa Barbara still lay beneath the ocean, but as more layers of sandstone and shale piled up in the Channel, in the form of granitic sands and fine mud, the floor rose, and Santa Barbara timidly peaked its sand and shale covered head above the ocean’s surface.

Perhaps you’ve noticed the red-colored rocks exposed along the base of the Santa Ynez Mountains, especially visible on San Marcos Pass Road several miles above Cathedral Oaks.  These are the Sespe “red beds”, a series of rock layers composed of shale, sandstone, and a mixture of pebbles and larger cobbles called conglomerate. The reddish color is the result of iron oxides within the shales and sandstones, a vivid celebration of Santa Barbara’s rise from its primeval depths.  It also leads geologists to conclude that this also was a period of tropical or subtropical climate, since red soils similar to these are being formed in the Tropics today. 

With the subduction ended, California now began to feel the first effects of the San Andreas Fault. When the subducting portion of the Pacific Plate moved north of Santa Barbara, it was replaced by a piece that began to slide against the North American Plate, a process which resulted in violent collisions.

The pressures built along the edges of these two plates, then were relieved suddenly in the form of earthquakes, releasing energy that began to lift thousands of feet of ocean sediments towards the heavens, making them into mountains. While the earthquakes raised mountains from the sea, erosive forces labored to wear them back down. Streams carried sand and gravel toward the ocean, forming the broad alluvial plain we now call the Sespe redbeds.  

For 11 million years this gently sloping land received deposits of sand, silt, and cobbles that would become the Sespe Formation. But rather than staying above water, almost as if in a last ditch effort to return to its marine origins, the land sank one last time. For another 10 million years the red beds were gradually buried under ocean-bottom sediments laid down in Miocene seas. 

The warm, shallow seas were more favorable to the development of marine life than at any other time. Small, single-celled organisms called diatoms flourished, as did many varieties of shellfish. Sea mammals, including whales, sea otters, seal, and sea lions evolved to maturity during the Miocene Epoch as well. 

Sediments included the layers we know as Rincon Shale, Vaqueros Sandstone, and the Monterey Formation. The latter two layers, heavily saturated with organic material due to the abundance of marine life, now play a very important part in Santa Barbara’s oil legacy. 

Eventually mountain-building processes initiated by our restless earth shoved these rock layers out of the ocean, this time for good, to form the land we live upon today. No doubt though, someday we will once again be part of an ocean floor. 

The Changing Climate
As Santa Barbara rose from the ocean depths, Southern California’s subtropical climate was beginning to shift to a drier, cooler environment. Approximately 13 million years ago, at the beginning of the Pliocene Epoch, rainfall, a staple of the evergreen forests and tropical plants such as the fern, lessened in its intensity and began to fall only in the colder months of the year. Colder ocean temperatures began to affect the positioning of the Pacific High and this blocked summer storms coming from the Alaskan Gulf, allowing them to occur only during winter and early spring months. 

As the cooling, drying trend accelerated, mixed conifer and subalpine forests began to adapt to a narrowing range of environments, becoming situated in small pockets and botanical islands,  either in areas of high relief or abundant rainfall, where drought stress could be avoided.

By the beginning of the Pliocene, open grasslands replaced the retreating forests, and as the Santa Ynez Mountains formed, they and other coastal ranges became important reservoirs for the survival and persistence of plants derived from the northern temperate rain forests. In addition, the uplifting of the Sierra Nevada began to protect coastal areas from even more intense periods of cooling and drying east of the Sierra, thus allowing the persistence of a number of relic plant species in Southern California.

Because of the climatic changes, another vegetative community much more suited to a developing mediterranean environment spread toward California from the East. Fifty million years ago, as the layers now forming the basic rock units of the Santa Ynez Mountains were being laid down in the Santa Barbara Channel, live-oak woodland and associated woodland trees such as the madrone, bay, and pinyon pine appeared as far west as the Rocky Mountains. By the Miocene, some twenty to thirty million years later, they had assumed dominance over the interior of much of Southern California.  

Another ten million years later, during the Pliocene, grasslands and an oak-woodland setting covered most of Santa Barbara County, a land of soft rolling hills, luscious clumps of perennial grass, and thick clusters of oak trees—not unlike the Santa Ynez Valley on an April afternoon today. It was not the home of cattle, however, but of prehistoric land mammals such as camels, rhinos, three-toed horses, hedgehogs, and other exotic species that thrived then on the wide expanses of grass.

As the Santa Barbara basin continued to fill with cobblestones, gravels, sand, silt, and other matter, these alluvia formed either rich, deep topsoils or in areas where shale predominated, were compacted to form dense clayey soils. In the areas of good topsoil, grasses became the primary ground cover, with native bunch grasses covering most of the coastal plain. The clay soils, less hospitable, tended to support a combination of grasses and woodland.

The first oaks to migrate to the west coast were of the temperate forest, primarily deciduous oaks which originated in the cool, wet forests of the northern half of the continent before being driven from the Plains, across the Rockies, and into the West. These migrating oaks were a mixture not only of deciduous, but also evergreen varieties  such as the California coastal live oak, which evolved in a much drier environment, most likely similar to that of the warmer drier parts of northern Mexico.

Today both the deciduous and evergreen varities of oak are an integral part of what we call the Santa Barbara landscape.  Valley oaks, the largest of the American oaks still thrive in the deep, moist soils of the interior valleys, though where people inhabit the valley floors, they are becoming an endangered species. Gnarled little blue oaks cover the grassy foothills surrounding the valleys, somehow getting enough moisture from the shallow soil to hold their leathery leaves through the dry summers. Living on stream flats or ravines where the topsoil is deeper and the moisture a bit more abundant are the equally gnarled interior live oaks, distinguished by having a greener foliage than the blue oaks. Higher on the slopes, where the grasslands give way to fir and pine, are California black oaks, a deciduous species with leaves similar in appearance to the valley oak but having needle-like points at the ends of the lobes. Along the coast, forming huge oak forests in places such as Hope Ranch or Montecito, the California live oak is the prevalent species.  

The drier climate also fostered the evolution of chaparral plant communities in Southern California. Able to survive in wetter climates, chaparral plants thrive in areas where dry, mediterranean environments prevail.

Perhaps the chaparral plants could be likened to hitchhikers, thumbs out, riding tectonic plates north into a more profitable environment, as movement along the San Andreas Fault caused Southern California to drift northward, with forces exerted by this movement generating a power almost impossible to comprehend, ripping Baja California away from the mainland and creating a trench between it and the Mexican mainland that would become the Gulf of California. 

Also breaking up the 30,000-foot thickness of sediments that had built up in the Santa Barbara Channel, it pushed them more than a mile in the air, twisted the entire block from its original north-south direction to the east-west orientation it has today, and moved the  Santa Barbara land mass with its newly evolving drought-resistant plant community toward an environment whose  mediterranean climate would allow them to thrive.

This mountain-building process began to occur about three million years ago, during the Pleistocene Epoch, uplifting the Santa Ynez Mountains to their greatest relief, perhaps as much as 7,000’ in height, as the tectonic pressures being exerted by slippage along the San Andreas Fault caused layers of sedimentary rock in the Santa Barbara area to turn on their edges along the Santa Ynez Fault. 

At this time a cooling trend also developed throughout the Northern Hemisphere, causing the onset of a series of ice ages.  Sheets of ice up to 10,000 feet thick covered much of the continent and the ocean level dropped about 350 feet. This caused the  coastline to retreat between 5 and 6 miles and exposed the Channel Islands as one long land mass. For several million years the climate in Southern California was cool and wet. 

Protected by the Sierras, the west coast endured not ice but torrential rain, which ate away at the rising mountains and provided the County with an environment much more like that of Monterey today, a period of rich and diverse plant life. Intermixed were conifers, redwoods, and deciduous woodlands. It was a period of pre-eminence in the Santa Barbara area for ferns such as the maidenhair.  

The Pleistocene Epoch  was not one long period but a series of recurring cool-moist, warm-dry cycles in which there was a constant reassortment of the two primary elements: the temperate forests of the north and the drought-resistant communities from the south. Some plants sought safety in the high country; others in the canyons, or on the flanks of the developing mountain wall. Those, like the maidenhair fern, did not seem to mind sharing chaparral country as long as it could receive a share of the meager rainfall. 

The overall trend, though, was one of drying, and after the Pleistocene ended, a warmer, less moist climate prevailed, allowing the spread of more drought-resistant plants like the chaparral into Southern California, and causing the  elimination of the primeval forests and the ferns from the low country.  

This warming forced the development of narrower, more specialized local environments, causing plants to separate into distinct plant communities.  Woodland forests  segregated themselves into ecological islands where they could continue to exist. Alder, sycamore, and maple migrated to the canyons. While coniferous forests shifted to the mountaintops, evergreen oak species migrated onto the thin coastal strip. Other woodland species, which required either a colder climate or more rainfall, such as the cottonwood and valley oak, retreated to more equitable climates found in the interior valleys and the backcountry.

Perhaps 10,000 years ago, as the Pleistocene cycles gave way to the development of a mediterranean climate, ferns removed themselves to the hidden places like the Playground. For the time being, at least, it was the era of the chaparral.

Soon the first humans, also in search of more hospitable environments, would be migrating to the South Coast.

    Sorry - nothing has been added yet.

Tuesday, July 28, 2015