Rocks!

Coleman Valley Road, Occidental
to Arch Rock Beach
Carmet, CA
Sonoma County

Occidental is a one drag town with three bars, a couple restaurants and home collectible stores. I have been told that at scene from Hitchcock's "The Birds" was filmed here, but I have not confirmed the same to be a fact. Maybe it was Vertigo ... but I digress. From the main street in Occidental there is a road called, Coleman Valley that heads west out to the coast. The drive is crooked and winding and if you don't happen to see the small hand painted wooden directional sign that reads "Ocean" you may miss the turn and head south towards the Bodega Highway. The drive out to the coast takes approximately thirty minutes from Occidental, but the drive goes quickly and the scenery is lovely--picturesque even. Barns, an old school house and cows dot the landscape as you drive through densely wooded expanses and into open meadows on your way to the apex of the hills. Once atop the rolling range, the scent of California sage brush lightly floats in the air indicating that the coast is near!


Soon enough the sage gives way to unencumbered green hills with few trees & shrubs gathered only around small waterways. A few granite outcroppings (rocks!!) can be seen which are indicators of ancient subduction zones. Subduction zones occur when two plate boundaries meet & converge. The more dense plate sinks or is subducted underneath the more buoyant plate. Oceanic crust is denser than continental crust and therefore is subducted under the continental plate to be absorbed back into the mantle. As the sinking plate is subducted the rock material breaks down, water is released which lowers the melting point of the mantle to produce magma. This magma then rises towards the earth surface and can result in a volcanic eruption. Over geological time the magma chambers cool and crystallize forming rock such as granite. As the materials around the chambers erode over millions (MILLIONS) of years, the granite becomes exposed. The granite in the Seirra Nevada's is estimated to be approximately 100 million years old--closer to the coast the rocks are dated at approximately 60-90 million years old. The next time you see a granite outcropping it is likely the site of an ancient volcanic arc--presently viewing the past.





The descent from Coleman Valley is a severe and dramatic drop to a little town called Carmet just south of Jenner. Carmet is home to Arch Rock Beach where many sea stacks and sea arches can be observed. Sea stacks and arches are the remnants of headlands worn down by wave energy. Sea arches form when the waves are directed around the end of a headland and crash on both sides form sea caves which eventually meet up! Once the sea arch falls, it becomes a sea stack. Stacks and arches are evidence of where the headland boundary once lived!



Photos = Joshua R. Neely