Stones of Santa Barbara County - The Geology of the Mountains of Santa Barbara
Nestled between the Pacific Ocean and the Santa Ynez Mountain Range, the Santa Barbara area is a place of many interesting rock formations.
The climate of this region is considered Mediterranean with mild winters and warm summers. Generally there is very little rain between May and October with the exception of occasional August and September showers.
More than 40 inches of rain may fall in the mountain areas during the winter months though perhaps only about 15 inches falls on the coastal plain of Santa Barbara. Every few years the highest peaks are dusted with snow that usually disappears within a few days.
A notable feature of these mountainous regions surrounding Santa Barbara are the warm sundowner winds that buffet the downslope areas sometimes quite forcefully.
This sundowner wind is more properly known as a foehn wind, which is a dry wind that forms on the downward side (lee side) of a mountain range and blows down the slopes. These foehn winds are also called rain shadow winds, and they are caused by adiamatic warming of air losing the preponderance of its moisture on a mountain’s windward slopes.
Since dry air and moist air have vastly different adiabatic lapse rates, the leeward air becomes much warmer than the windward air at the same elevation. A foehn wind can increase temperatures up to 54 degrees Fahrenheit in just a few hours.
The scenic mountains of the Santa Barbara region and the broad coastal plains provide a unique array of geological landforms, stone formations, and other features that include rocks more than 50 million years old.
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Santa Barbara’s Oldest Rocks
The oldest rocks of the Santa Barbara region are revealed in huge outcroppings and rocky ledges that have been turned up on their sides exposing surfaces which allow geologists to see back in time. The tumultuous geological profiles reveal faulting, folding, and uplifting of the massive rocks of the Santa Ynez Mountains.
Originally formed as ocean basin deposits, the rocky formations eventually rotated more than ninety degrees counter clockwise and then pushed upward to form the coastal ranges.
During the last half million years this faulting and uplifting produced the Santa Ynez Mountain Range as well as other formations along the coast.
Scientists have been able to pinpoint the times that various ranges were formed through uplifting by examining the lowland sediments and extrapolating from known erosion rates. In addition the sea level was rising and falling, inundating the whole Santa Barbara area about every 20,000 years.
Santa Barbara’s Geologic History - How Were the Mountains Formed?
Beneath much of the Santa Barbara area are basement rocks that are considered to be part of a mix of deep water sedimentary rocks that are known as the Franciscan Formation.
This formation is composed of a mix assemblage of rocks including sandstones and cherts (having been deposited on the ocean floor) as well serpentinite and basalt (chunks of the ocean’s crust).
When the Pacific Plate subducted, or dipped beneath, the North American Plate, the rocks of the formation were pushed up onto the edge of North America.
Much of the Santa Ynez Mountain Range is comprised of Eocene rocks that are marine in nature with a thickness in some areas of more than 10,000 feet.
Sitting atop the Eocene marine rocks is the Coldwater Foundation that consists of about twenty percent siltstone and shale and about eighty percent sandstone, and it is the most resistant sandstone that now forms the range’s highest peaks while shale is more common in the valleys.
Eventually the ocean withdrew and exposed the coastal plain, and onto this broad plain were deposited conglomerates, silts, and sandstones that were all part of the Sespe Formation, a non-marine formation which is most coarse near the base where the sandstones and conglomerates are inter-mixed.
The Sespe Formation is red in color due to oxidation of iron in the sediments. Eventually the ocean again covered the area creating the Vaqueros Formation which is rich with shell material and covered by marine shales and siltstones.
A top the Rincon Shale is the Monterey Formation rich in organic debris that subsequently become oil and gas deposits, thus the drilling in the channel and the finding of tar chunks on the beach due to tar seeps.
Also rich in shells is the Sisquoc Formation near UCSB and Goleta shoreline, and comprised of gray mudstone.
Uplifting and faulting of the accumulated rocks created the Santa Ynez Mountains which proceeded to erode and send debris of alluvium onto the coastal plain along the base of the mountains. This uplifting and reshaping of the land continues today, as does the erosion.
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Santa Barbara Geology Today
Today the faulting and uplifting of the Earth continues, and lowland sediments continue to be deposited in many areas, even forming huge hills such as 800-foot (and growing) Mission Ridge just to the north of Santa Barbara’s downtown.
Earthquakes cause uplifting of former beach areas that creates terraces known geologically as stair-step topography. Because of the rapid uplift rates in the area (e.g., about 3.5 mm per year on average), the Santa Barbara region has some of the youngest marine terraces.
The Santa Ynez Mountains and the Transverse Ranges
The Santa Ynez Mountains are one of the Transverse Ranges of Southern California, part of the many mountain ranges stretching along the coast of North America from Mexico to Alaska.
The name Transverse comes from their unique east to west orientation that is quite different - indeed transverse - from the south to north orientation of other mountain ranges along the Western coast from Mexico to Alaska.
The reason for this transverse quality is due to a bend in the San Andreas Fault which forms the boundary between two of the Earth’s great tectonic plates, the North American Plate and the Pacific Plate.
This bend causes huge pieces of the Earth’s crust to compress and lift, and over time this has shifted the whole orientation of the mountain ranges.
The Santa Ynez Mountains run parallel to the Channel Islands to the south which also trend east to west.
Along the Santa Ynez range are Santa Ynez Peak (4,298 feet), La Cumbre Peak (3,985 feet), and Divide Peak (4,707 feet). In ancient times this whole area was home to the Native Americans known as the Chumash.
Atop San Marcos Pass is the Cold Spring Canyon Arch Bridge which connects Santa Barbara with Santa Ynez. The bridge opened in 1963 and near the bridge on Stagecoach Road is the Cold Spring Tavern at a site that was one of the original stagecoach stops.
The Santa Ynez Mountains are predominantly sedimentary having been initially lifted up some five million years ago along the Santa Ynez Fault. The steepness and ruggedness of these mountains, featuring huge sandstone formations, is attributed largely to their relatively young age.
Along the Santa Ynez Mountains’ northern hills are areas of mixed woodlands along with oak savanna. The mountain range is covered with lots of chaparral while the lower elevation areas are mostly grasslands, coastal sage scrub, and oak woodlands.
On the upper areas of the northern slopes of the Santa Ynez Range are some lone stands of conifers and other evergreens including tanbark oak, bay laurel, and madrone. On the warmer and less rainy southern slopes now home to many avocado orchards.
Areas atop the ridge of the Santa Ynez Mountains provide a great view of the Pacific including all seven Channel Islands. One of the most famous ranches in the Santa Ynez mountains is located in the mountains just west of Santa Barbara and was owned by Ronald Reagan.
Rock Art of the First Santa Barbara Natives
The Native Americans who lived in the Santa Barbara region from ancient times are known as the Chumash. They created a wide variety of useful tools and crafts, and also left extensive rock art that still exists at remote and protected sites in the area.
Some of the most beautiful rock art of the Chumash is located in the Painted Cave area near the top of San Marcos Pass in the Santa Ynez Mountains.
Painted Cave is a small community located about two miles off of Hwy. 154 (San Marcos Pass), and 5 miles from Hwy. 101 and about 11 miles from downtown Santa Barbara. Painted Cave consists of about 100 homes with more in the outlying regions.
Some beautiful Chumash rock art is preserved nearby in Chumash Painted Cave State Historic Park which consists of a small cave comprised of sandstone and decorated with art dating to ancient times.
Mineral pigments and other substances were used to create elaborate drawings that are thought to reflect the cosmology of the Chumash. The historic and culturally important cave site was listed on the National Register of Historic Places in 1972.
The rock art of the Chumash people contains many images including celestial bodies, a variety of shapes and patterns, human-like images, and also animals.
The paint used for Chumash rock art was created by mixing stone mortar with mineralized soil. To this a liquid binder was added, and this may have been composed of mashed seeds or perhaps oil from animals or even blood.
The purpose of the binder is to create a permanence to the paint and also make it waterproof. Whatever was used was very effective as the rock art of the Chumash has lasted a very long time in many places.
The distinct colors of this stunning Santa Barbara rock art came from many sources including kaolin clays (white), manganese or charcoal (black), serpentine and copper (white), limonite (blue), and iron oxide or hematite (red and orange).
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