Geology of the California Channel

The dramatic mountains that are the mainland backdrop to the Pacific Channel Islands offer the viewer a time line marked by dramatic geologic events. When one traces the northern Channel Islands back to the shoreline, it is possible to realize that the islands we see today are the tips of mountains that are the westernmost part of the Santa Monica Mountains, running parallel east to west with the Santa Ynez Mountains that are behind Santa Barbara. The northern and southern Channel Islands are actually part of the continental shelf - the land mass that is the continuation of the mainland that runs out under the ocean.

What these mountain ranges tell us - both as inland ranges and as island formations, is that there has been tremendous geologic forces at work on this edge of the American continent for hundreds of thousands - even millions - of years. Scientists estimate that around 15 million years ago the Channel was a hotbed of volcanic activity - much like Hawaii is today. Over the years, the Channel Islands have been formed through a combination of volcanic activity ( pushing molten magma to the earth’s surface - in this case at times underwater ), erosion from the sea as ocean water levels have risen and lowered as much as 300 feet during different ice and warming ages ( wearing away the islands as a result of surf and tide conditions ), and seismic activity ( the lifting and folding associated with earthquakes and other long term movements of the earth’s crust ).

Inland on the north side of the Santa Ynez mountains, fossils of sea shells are easily found along dusty trails through the hot, parched chaparral where it is hard to image the sea ever reached. But it did, and when the sea deposited those fossils inland, the forces of nature were very different than what we know today.

The Pacific Ocean has a deep rift, or open canyon, down the center. From that center nearly consistent pressure is applied from the molten forces within the earth that then move up towards the crust, and then push it out and away from these canyon rifts. As that pressure is applied, the Pacific’s floor then is forced to move, sliding the plate of the ocean floor east up against the mainland, which as a continent is at the same time being pushed towards the west by similar forces from the Atlantic rift. When these two geologic formations collide, dramatic things occur - earthquakes rumble, mountain ranges are lifted up thousands of feet, deep valleys are formed, water courses change, and the very minerals that compose the earth are reshaped again and again.

Much of the Channel Islands and the mainland is made up of sandstone - sand from the sea floor that has undergone tremendous compression from the weight of the sea above it. Then when this sandstone is exposed by changes in sea level, we see its beauty and the many fossils it holds. But sandstone is not the only geologic formation in the Channel region. Santa Barbara Island is actually the tip of a Miocene volcano ! And Miocene volcanic rock occurs on San Miguel, Santa Rosa, San Clemente, Santa Cruz, Santa Catalina, and all of Anacapa Island is primarily Micocene volcanic rock uplifted by seismic activity.

San Clemente Geology Santa Catalina Geology San Nicolas Geology Santa Barbara Geology Anacapa Geology Santa Cruz Geology Santa Rosa Geology San Miguel Geology

Channel Earthquake Faults

The region is lace with faults, many running out into the sea from the mainland, others on the islands themselves. These faults are places where the earth is experiencing tremendous conflicting forces as the surface plates are forced in opposite directions, at times colliding, at other times slipping past each other. The disastrous earthquakes of California are well known world wide, and have resulted in devastating freeway collapses, fires that have swept through entire cities, tidal waves, buildings slipping into the sea, and loss of life and buildings on a massive scale. They are also the reason an entire native island population moved from the Channel to the mainland Santa Barbara Mission in 1812.

The force of the Pacific tectonic plate moving into the mainland of western American is a force we can not control or stop. What can be done is live in preparation for earthquakes, and to support scientists who are developing earthquake detection methods for early warnings.

Oil and Gas Deposits

In the Santa Ynez Mountains, one can see flat oceanbed sandstone that has been lifted to a vertical position and folded down again directly beside it. The geologic forces that must have been applied to this rock strata, once a flat horizontal surface and now a vertical incline and immediate decline, are quite mind boggling. And it is these such visual records that hint at the underground oil reserves that have been the boon and the bane of the Channel region. For reportage on the controversy over oil subsidies, click here.

The ‘discovery’ of large oil reserves beneath the Channel was not the accomplishment of solely modern geologists. Native Americans for thousands of years have been harvesting the tar that seeps from the ocean floor and floats up onto the surface, then washing ashore with the tides. This tar caulked their boats and cooking baskets, mended their stone bowls, and was the adhesive for decorations on cave paintings, pipes, bowls and stone effigies.

In written history, a sea captain, George Vancouver, wrote in 1793 that as he passed through out the Channel there was a film of ‘ dissolved tar ‘ as far as the eye could see. And by the late 1800s, entrepreneurs were drawing people to Santa Barbara to partake in the then-touted healing fumes from the gases that seep out from the ocean floor along with the tar.

Oil Seeps

Along the northern margin area of the Channel, geologists have located an estimated 2,000 oil, gas, and asphalt seeps. Coal Oil Point, ten miles up shore from U C Santa Barbara is thought to be the largest natural underwater oil seep in the world.

The reason for these seeps is that the sea floor in the Channel is perforated with holes, some over three feet in diameter. Through these escape hatches, oil and gas bubble up in huge volumes, creating what divers have called a ‘sea of champagne’. An average of 50 barrels of oil penetrate the ocean floor each day at Coal Oil Point alone. The little amount of sea bed covering that deposit is weak and crumbling shale, easily pushed aside under the geologic forces that are steadily pushing the oil to the surface.

The California State Lands Division estimates an average of 25 barrels of tar can be found on Santa Barbara Channel beaches on any given day. For a historical over view of the oil development in the Northern Channel region, click here.

The Geology of Oil

But where does all of this oil, tar and gas come from ? Why is it here, under the Channel and along its shores in Long Beach ( one of the largest oil discoveries in history ), Ventura and Santa Barbara, rather than other places ? How do geologists know where to find oil ? What happens when it is extracted ? Will it last forever ?