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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.

Present-day Active volcano 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 is surrounded by deep rifts from which nearly consistent pressure is applied from the molten forces within the earth that 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 is forced to move, sliding the plate of the ocean floor -and a portion of California which is connected to the Pacific Plate- north and grinding it against the mainland, which as a continent is at the same time being pushed towards the west by similar forces from the rift in the center of the Atlantic ocean. 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.

Santa Rosa Island 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.

Oil in the Channel

Earthquake Faults

San Clemente Geology

Santa Catalina Geology

San Nicolas Geology

Santa Barbara Geology

Anacapa Geology

Santa Cruz Geology

Santa Rosa Geology

San Miguel Geology