THE MAKING OF CALIFORNIA--PLATE TECTONICS VS. MOTHER NATURE’S WEATHER AND EROSION, PART 1: PANOCHE ROAD
California’s Coast Ranges that stretch along its coast all the way from the Oregon border to the Los Angeles coastal plain were formed by the collision of the Pacific tectonic plate and the North American tectonic plate over tens of millions of years. About 250 million years ago the Pacific Plate, pushing the smaller Farallon Plate in front of it, began its collision with the North American Plate. The sea floor crust of the Farallon Plate and then the Pacific Plate slipped beneath the North American Plate, heating and melting as they were pushed deep into the Earth. The plates melted and the molten rock formed volcanoes like Mount Shasta and the molten granite that formed the plutons of the great Sierra Nevada batholith.
As the slow motion collision progressed, arcs of islands similar to the islands of Japan today formed from local volcanic action on the Pacific Plate and were carried eastward toward the North American Plate shoreline. They crashed into it and attached themselves, making new mountains along what was then the coastline. The islands and submarine deposits riding on the Farallon and Pacific Plates were scraped off by the edge of the North American Plate and were deposited on the edge of that Plate, forming the beginnings of the Coast Ranges.
About 20 to 30 million years ago the Pacific Plate changed from a head on, more or less east-west collision, to a lateral movement, slipping against the North American Plate generally along the line of the San Andreas Fault. Folding of the sea floor along the fault contributed to raising the Coast Ranges and, near Los Angeles, the Transverse Ranges. These ranges are composed of the crushed and folded sea floor sediments of the Pacific Plate eroded by millions of years of rain and wind.
All of this colliding, subducting, erupting, twisting, folding, eroding and repeating, again and again, created the very complex, diverse and, in many instances incredible, landscape of California.
The process is, of course, like the resulting rock formations, confusing, and, because it takes place over millions and millions of years, very hard to visualize. Which mountains came first? Why are these different from those? And so on. Unfortunately, there is no time lapse movie taken from a few hundred miles about the surface of the Earth over the last 300 or 400 million years so we can see exactly what happened where and when. But there are places we can visit and get a feel for the almost miraculous geological process that made the place we call California.
This The Real Mr. Science story, and a few that will follow, will explore some of those places. The first of the places we will explore is the Panoche Valley area in middle California, almost due east of Monterey Bay. All the recent geological processes that built California have examples in the Panoche area. Fortunately, the area can be accessed in dry weather by a family automobile via Panoche Road and others in the area, so you can go there and see it all for yourself. A map of the Panoche area courtesy of the Bureau of Land Management can be seen here: Click here for Map.
By the way, as far as The Real Mr. Science can tell, there is no other place on Earth with the name “Panoche.” Most place names, even the unusual ones, apply to multiple locations, but not so for “Panoche,” which is believed to be derived from a local Native American tribe’s word for a species of sugar cane that once grew in the Panoche Valley.
We will start from the eastern end where Panoche Road intersects Interstate 5 about 15 miles southwest of Firebaugh, California. There is a motel, restaurant, small food mart and gas stations at this freeway exit. Be sure to gas up before leaving. It is 60 miles to the next gas station in Hollister, even if you do not visit some of the other interesting places along the way.
Panoche Road enters the gentle rolling hills of the Panoche Creek area and winds along Panoche Creek in a series of gentle valleys. These hills were created by the piling up of the marine sediments resting on the Pacific Plate as it and the North American Plate collided. Folding and faulting pushed the hills up, so that marine layers now lie 1,200 feet and more above sea level. Over millions of years periods of pushing up, folding and faulting, rain and wind raised and then eroded the hills and smoothed their contours, masking the grinding collision that was their birth. The pavement on Panoche Road ends not far into the valley, but the dirt road is well graded. There are no significant alternative turns. Wildflowers in season and cattle in open range are along the way.
Pic 1: Looking East: Panoche Valley From Jackass Grade
Take a moment to get your bearings. To the north (left side) are the Panoche Hills. To the south (right side) are the Tumey Hills. Panoche Road passes more or less between them. The road bears southwest and begins to follow Silver Creek, a tributary of Panoche Creek in a narrowing canyon. It then gently climbs out of the Silver Creek valley and then more steeply up “Jackass Grade.” In dry weather this is a moderate climb to about 1,300 feet in elevation on a smooth dirt road, but in wet weather it would be difficult due to the slick clay surface in places.
Pic 2: The Tumey Hills Also Seen From Jackass Grade
About two-thirds of the way up the grade, there are two switchbacks and between them there is a wide, fairly flat spot on the road. The pull out permits you to stop and explore. The view alone is well worth stopping for: the curved pattern of the hills and valleys, the shadows and the grasses waving in the wind, but the local geology is even better. Click this link to a video of Panoche Road East from Jackass Grade.
These hills are sedimentary in origin. They were ocean bottom until elevated by the collision of the tectonic plates, and then folded so that the former ocean floor now tilts skyward. Erosion and road cuts have exposed a large variety of rocks that are part of the ocean floor sedimentary deposits. Many look like the stones you might find in the bottom of a river. That is because they were exactly that until perhaps 20 million years ago when the plate collision raised them to 1,200 feet above sea level. These were the stones shattered and polished in the ancient rivers that flowed down into the sea at what was then the California coast line. Washed onto the continental shelf along with sand and other sediments, they settled in the layers that time and pressure would turn into sandstone. Erosion and a road grader have revealed their secret existence.
Pic 3: Greywacke (sedimentary rock with embedded river rocks)
Pic 4: Delphinium gypsophilum, Pinoche [sic] Creek Larkspur. The species name means "gypsum-loving," and there's certainly a lot of gypsum in this area. A wildflower indigenous to California. Photographed just off Panoche Road on the eastern side of Jackass Grade. (Note: highly toxic.)
Pic 5: Layia platyglossa, Coastal Tidy Tips West of
Pic 6: Castilleja franciscana, Franciscan Paintbrush (aka Indian Paintbrush)
Pic 7: Orthocarpus densiflorus, Owl's Clover West of Jackass Grade
At this point Panoche Road is joined from the south by the New Idria Road. The intersection is well signed.
Pic 8: New Idria Sign
Pic 9: The Road to New Idria Climbs Into the Hills From The Floor of Panoche Valley
The New Idria Road follows Los Aguilas Creek into Griswold Canyon. There are sandstone formations that are part of the late Mesozoic Franciscan Formation Complex. The Complex consists of sandstone called greywacke because a mixture of other minerals causes the sandstone to be slightly grayish. The name comes from the German word grauwacke, first applied to it by German geologists. In places the sandstone layers contain layers of bumps of harder material exposed by erosion.
Pic 10: Embedded Rocks Forming Bumps in Sandstone
Pic 11: Embedded Rocks in Faulted Sandstone
The sandstone also shows regular formations of harder round rocks deposited in layers during the marine river period of its formation. Massive floods of water from the rivers would occasionally come down onto the sandy marine bottom depositing a layer of river eroded and smoothed rocks later covered by more layers of sand. Their elevation from marine environment to a hillside in the Griswold Hills on the side of Griswold Canyon resulted from plate tectonics. The exposed rocks reveal the later stages of the collision process. There is a fine example of this layering almost on the opposite side of the road from a sign identifying the location as the Griswold Hills.
Pic 12: Layering in the Franciscan Formation
In other places the sandstone shows tafoni formations, deep, cup-shaped pits in the sandstone varying in size from a thimble to a basketball. This weathering is caused by salt crystallization and erosion. Moisture in the sandstone brings dissolved minerals, principally salt in the case of Griswold Canyon, to the rock surface. When the moisture carrying the dissolved salt evaporates from the rock surface and from the near surface, the salt crystals reform and force small particles of the sandstone to flake off. The salt was, of course, originally deposited in the sandstone by the sea water in which the sandstone formed.
Pics 13 and 14: Small and Large Tafoni Formations
The New Idria Road begins to follow Vallecitos Creek up stream and over the Syncline Divide into the valley of the Los Pinos Creek and then the San Carlos Creek, finally climbing to the site of New Idria on a hillside above the canyon. Along the way into New Idria the road climbs past exposed rocks of the Franciscan Complex. In places the faulting and folding has caused layers of the sandstone to be turned into a perfectly vertical position, 90 degrees from its original orientation.
Pic 15: Tilted Sandstone Formation With Both Tafoni and Embedded Rocks
New Idria is situated on the shoulder of one of the hills climbing out of Griswold Canyon. The little town surrounds the New Idria Mine mill works, last operated about 1970. New Idria, together with three other much smaller mines nearby, was America’s second most productive quicksilver (mercury) mine. It was named after one of the world’s most productive quicksilver mines—Idrija in Slovenia. New Almaden, just south of San Jose, California, was the first most productive in America and, incidentally, was named after a famous quicksilver mine in Spain. Californians anglicized the pronunciation and the spelling Idrija to its present Idria.
Pic 16: New Idria Sign
Quicksilver is extracted from the relatively rare cinnabar ore by heating it. New Idria was a pioneer in the process. Early in New Idria’s operations extraction was accomplished by heating the cinnabar in a brick oven-like structure. The quicksilver vaporized and condensed on the oven walls and floor. Miners entered the oven and scraped up the quicksilver. Since mercury causes serious health problems it was a very hazardous job indeed.
These are some pictures of New Idria Mine operations from early in the 20th century.
But a new and safer process was put in practice for the
first time in New Idria by innovative mine superintendent Henry Gould, who
adapted a cement-making furnace for extracting quicksilver. The Gould
Rotary Furnace was first used at New Idria and performed the same function as
the brick ovens (actually, it did a much better job), but it did not require
exposing the miners to the quicksilver or its fumes so extensively. The
Gould process is used even today, especially in making cement.
Pic 17: Gould Rotary Furnace Building
Pic 18: Output Chutes From Gould Rotary Furnaces
Quicksilver was so important because it was a key component in extracting gold from gold-bearing ore. Without New Idria and New Almaden, California gold would have been extracted from ore by using quicksilver imported almost exclusively from Europe, so these cinnabar mines were a very significant part of the California gold rush.
The site has remains of the ore stamp and furnace mill and a few wooden buildings, such as the local grocery store, and post office, but recent fires caused by vandals have destroyed many others. Stay out of the buildings, which are structurally dangerous and may have hanta virus in them. A panoramic picture taken many years ago shows the town in a less dilapidated state than today, shown in the modern video. Click here for a panorama video of how New Idria looks today.
Pic 19: Panorama of New Idria in the 1960s
New Idria was declared a Super Fund Site in mid 2011. Clean up will eventually make the site safely available to visitors. See the EPA's web page for details:
New Idria is both fascinating and sad. It was a key player in the gold rush although located a long way from the Mother Lode, but time and the vagaries of fate have not been kind to it.
A road called Clear Creek Road runs southwest from New Idria to Los Gatos Road near Hernandez Reservoir about 15 miles away. It is NOT suitable for a family automobile, but could be used by 4-wheel drive, high clearance vehicles; however, the Bureau of Land Management, which is responsible for this public land, has closed an area called the Clear Creek Management Area due to potential asbestos contamination, which may be caused by vehicle disturbance of the naturally-occurring asbestos in the serpentine formation rocks prevalent in the area. The infamous Atlas Asbestos Mine, which is now an EPA Superfund Site, is nearby.
Return to the junction with Panoche Road back through Griswold Canyon and travel west (left) on Panoche Road. You might stop at the Panoche Inn just a few miles from the junction of the Panoche Road and the New Idria Road. It has excellent sandwiches, homemade pickles, cold beer and soft drinks and a couple of very friendly hosts.
Pic 20: Panoche Inn
Panoche Road travels west through rolling hills with spring wildflowers and cattle until it reaches California Highway 25 at Paicines, which is pretty much just a store. Here, we can turn right (north) and drive to Hollister, just 10 miles away but, if time allows, we can see more of the results of mountain building due to the tectonic plate collision by turning left (south) and following California Highway 25.
South on 25 brings us past the eastern entrance to the Pinnacles National Monument. The Pinnacles are the heavily eroded remnants of an ancient volcano that forced its way up through the largely sedimentary rocks of the Gabilan Mountains. The Gabilans are the product of the scraping, folding and faulting of the sedimentary rocks of the Pacific Plate in its collision with the North American Plate. The relatively rounded shapes of the Gabilans mirror the Panoche hills but at a larger scale. Both resulted from the same tectonic activity. The San Andreas Fault runs along the eastern edge of the Gabilans and Highway 25 is located immediately in the rift zone. For a little fun click here to follow the fault on an interactive map.
The volcanism of the Pinnacles was caused by the melting of a part of the Pacific Plate as it was subducted under the North American Plate. The further under the surface of the Earth the Pacific Plate was forced, the hotter it got until it melted and became molten rock. The molten rock found a crack in the fractured rock around the faulting caused by the collision and pushed to the surface millions of years ago. The strange shapes, rocky slopes, sheer walls, monoliths and spires of the Pinnacles resulted from ages of erosion and folding working on the volcanic rock.
Pic 21: Pinnacles —Volcanic Rocks Intruding Through Granitic Formations
Pic 22: Pinnacles—Close Up of Volcanic Rock Mixed with Granite
The Pinnacles are also home to the California Condor, a huge raptor native to this part of California which, after having been near extinction, has been reintroduced to the area and is growing in numbers. They can sometimes be seen soaring on the thermals near the peaks.
Highway 25 continues to more or less follow the San Andreas Fault zone south before turning west toward the Paso Robles area and offers views of faulting and folding in many places along the way. A more exciting route, however, is to turn east (left) about 12 miles south of the Pinnacles onto Coalinga Road toward Hernandez Reservoir. Coalinga Road climbs over the shoulders of Black Mountain and Laguna Mountain down to the reservoir. Past the reservoir the road enters the valley of the San Benito River and winds down the valley for many pretty miles. Where Coalinga Road enters Fresno County its name changes to Los Gatos Creek Road. Do not be fooled.
Just below the Hernandez Reservoir on Coalinga Road, Clear Creek Road comes over the hill from New Idria to the east. A short distance up Clear Creek Road the closed zone established by the BLM begins. At Clear Creek Road’s ford over the San Benito River there is a small and moving memorial for a young local man turned soldier who was killed in the Viet Nam War and was awarded the Bronze Star and the Purple Heart -- Sergeant Raymond F. Eade. Even if you do not plan to go up Clear Creek Road, stop a moment and read the plaque placed there in his memory.
Pic 23: San Benito River Ford with Clear Creek Signs
Pics 24 and 25: The Eade Memorial
The riverbed at the ford offers an excellent place to poke round for rocks that started life as river rocks, washed on the continental shelf of the North American Plate, elevated to mountain height and then eroded down the river channel. Keep your eyes open. California’s State Gemstone, Benitoite, was discovered in February 1907 by prospector James Couch while searching in the area for cinnabar or copper ores. He could not identify the beautiful blue gemstone and sent samples to University of California professor who recognized it as a previously unknown mineral and named it Benitoite because it was discovered in the San Benito River area. So far it has been located only in this area. Benitoite is a barium-titanium silicate found in serpentine formations that have been exposed to hydrothermal water intrusion. A beautiful stone, since designated the California State Gem.
Pic 26: Benitotite
While topo maps show side roads up into the mountains to the east of Coalinga/Los Gatos Creek Road, those below Clear Creek Road appear to be blocked off or marked private. Following the valley road is very pretty and eventually leads you to the oil fields on the outskirts of Coalinga, with I-5 an easy 12 miles to the east.
Part 2 of our adventure in exploring the magic worked by plate tectonics will take us to the Carrizo Plain National Monument, where you can stand with one foot on each plate.
Pics #s 1, 2, 4, 5, 6, 7, 8, 9, 15, 16, 18, 23, 24, and 25 are copyright 2011 by E. Ahonima, and used by permission. More excellent pictures of the Panoche Valley by E. Ahonima are available on flickr. Click here for more E. Ahonima pictures.
Pic #19 made available though the courtesy of Wikimedia Commons, and subject to Wikimedia Commons Creative Commons License
Pic #20 Courtesy of Don Inamasu from his informative blog. Click: D. Inamasu
Pic #26 Provided by Didier Descouens, through Wikimedia Commons, and subject to Wikimedia Commons Creative Commons License
All text, videos and pics not otherwise attributed above are copyright 2011 by www.therealmrscience.net. All rights reserved. Contact: firstname.lastname@example.org