The Damning of Del Puerto Canyon

This stunning canyon is underneath severe risk

California geology is sophisticated. Not like every other state, it’s affected by the interactions of all three sorts of plate boundaries: divergent (the crust pulling aside), convergent (the crust compressing collectively), and remodel (the crust sliding laterally). All of those forces have shaped a posh panorama with unbelievable surroundings not like every other place on this planet.

The Coast Ranges province is a kind of distinctive areas. Extending some 400 miles from the Oregon border to the Transverse Ranges close to Level Conception, it is among the least acquainted components of California (except for the Pacific Freeway 1 hall by way of Massive Sur and the Marin Headlands/Level Reyes area). The province is outlined by a collection of particular person mountain ranges that development roughly parallel to the coast, however the variation in rock varieties and construction is astounding. Throughout the province there are active volcanic fields, older inactive volcanoes, huge tracts of tilted sedimentary rocks, exposures of twisted and folded rocks shaped deep within subduction zone complexes, and even a displaced section of Sierra Nevada granitic crust. Quite a few energetic faults slice by way of the province, together with a lot of California’s most harmful: the San Andreas, the Hayward, the Calaveras, and lots of others.

We simply explored the guts of the satan: the so-called Diablo Vary. It is among the largest particular person ranges within the province, operating for round 150 miles from Mt. Diablo and the Carquinez Strait on the north to the Coalinga space within the south. The area is essentially undeveloped, and few paved roads cross vary. We adopted a kind of few roads, the one which traverses Del Puerto Canyon. It is a one-of-a-kind expertise, the equal of driving into and thru the crust of the Earth and into the mantle under. It’s the path to the nether-world that has typically been known as the house of the satan.

Del Puerto Canyon lies simply west of the Central Valley city of Patterson. A paved street, state route 130, connects Patterson with the Santa Clara Valley, however anybody considering it could make a shortcut between the 2 localities is in for a impolite awakening: curvy, slim, with steep drop-offs, it isn’t a street for the faint-of-heart. It additionally has some extraordinary surroundings and a few completely fascinating geology.

The decrease canyon exposes 25,000 toes of late Mesozoic and early Paleogene marine sediments deposited within the forearc basin of the Cordilleran subduction zone that stretched the size of California. The center stretches reveal the oceanic crust on which the sediments had been deposited, the Coast Vary ophiolite (the second-most full part present in California). The uppermost canyon is the strangest atmosphere of all, consisting of rocks that had been as soon as a part of the Earth’s mantle. The rocks are fascinating, and so are the vegetation that survive on the ultramafic soils.

One in every of our college students found an ammonite fossil on this journey!

The canyon additionally has a spot within the historical past of California paleontology. The 25,000 toes of oceanic sediments present an in depth report of fossil species, together with the clams, snails, ammonites and shark enamel which are anticipated in such environments. Mesozoic marine reptiles have additionally been discovered within the area, together with plesiosaurs, ichthyosaurs, and a brand new species of mosasaur, Plotosaurus bennisoni. The canyon was additionally the location of the invention of California’s first dinosaur, a species of duckbilled dinosaur known as Saurolophus. It was found by 16-year-old Al Bennison of Gustine in 1936. We discovered a single fossil this journey, an ammonite. Sometime, it will be a dinosaur, proper?

To me, essentially the most fascinating rocks are discovered within the higher canyon. The mantle of the Earth is a 1,800-mile-thick layer that begins at a depth of 15 or 20 miles beneath the continental crust. It’s usually composed of a rock known as peridotite or dunite, made up of the mineral olivine with various quantities of pyroxene and numerous ores of chrome, mercury, magnesium, and copper. Peridotite is chemically unstable in floor circumstances and alters principally to serpentine. Lots of the rocks we noticed confirmed a point of alteration. The rock under that appears like alligator pores and skin (under) consists of fractured chunks of pyroxene (the reddish-brown) and serpentine (the inexperienced fracture filling).

In just a few spots one can discover some comparatively unaltered peridotite (under).

We additionally discovered some samples of chromite ore. Chrome contributes to the manufacturing of stainless-steel and has purposes in forming armor. Throughout peacetime, there are cheaper sources of chrome abroad, however throughout wars the provides could also be lower off. Throughout the world wars, chromite was mined within the higher canyon and transported by rail down the canyon to Patterson to be processed.

The little black grains are chromite

The higher canyon was additionally a supply of cinnabar, a mercury sulfide mineral. Regardless of its poisonous nature, mercury was a vital element within the processing of gold ores through the Gold Rush. Miners might typically make a very good wage mining the ores, however they might achieve this at nice threat to their well being. Fortunately the temptation to assemble mercury ore was not attainable because the mine properties are fenced off.

The final a part of our journey is the saddest. The decrease canyon, the primary five-and-a-half miles, is underneath risk. An area irrigation district is intent on constructing a reservoir that can flood a lot of the canyon underneath a whole lot of toes of water. It’s going to serve no function apart from to retailer extra water from the California Water Undertaking (within the uncommon years when such extra is out there). It could then be utilized in subsequent drought years. In different phrases, it could be an evaporation pond, a waste of water. There can be no leisure amenities. Quite a few archaeological websites can be flooded, and treasured prairie and riparian ecosystems can be destroyed.

There are geological considerations. The dam itself can be constructed 1 / 4 mile from a doubtlessly energetic fault system (there was an earthquake swarm within the canyon earlier this 12 months). There are seven gigantic earthflows and slumps, one a mile lengthy, that may be partially inundated and doubtlessly reactivated. And it is true I am not an engineering geologist, however I query the soundness of the shale, siltstone and sandstone that the dam abutments can be anchored in. I wasn’t reassured by the environmental influence report.

In any case, there’s neighborhood opposition to this misguided plan. It’s going to do nothing to profit the area people even whereas it threatens close by cities. If you want to study extra, and assist efforts to cease this boondoggle challenge, please contact the group Save Del Puerto Canyon. It could be such a disgrace to destroy yet one more stunning place in service to financial advantages for the only a few.