I’ve written before about the geology of southern California here, here, and here. It’s a subject that fascinates me, in part because this is where I call home, and because of the spectacular land that has resulted.
The Vasquez Rocks are the result of the uplift of the San Gabriel Mountains from the tectonic interactions of the North American and Pacific plates starting about 25 million years ago. The forces generated by the movement of these two plates resulted in extremely rapid uplift, but also extreme fracturing of the rock material. It has been suggested that the San Gabriel Mountains are among the fastest rising mountain chains on Earth, while simultaneously be among the most quickly eroding. It is this erosion that led to deposition of the sediment that would eventually become the formation we know today as the Vasquez Rocks.
As the growing San Gabriel Mountains began to erode, sediment began to accumulate to the north and south. Along the southern edge, these sediments began filling deep basins, eventually forming what we today call the Los Angeles Basin. Similar activity occurred along the northern edge, and eventually the sediments that would eventually become the Vasquez Rocks were buried. Subjected to enormous pressure and heat, these sediments were welded into sedimentary rock that was eventually exposed through erosion as activity along smaller faults paralleling the San Andreas fault began the process of uplift.
As this sedimentary rock was buckled, deformed, and tilted on its journey from below the surface, softer material was eroded away by wind and water to expose the extremely tilted rock structures that today make-up the Vasquez Rocks. Since sediments are laid down in thin discrete layers, today’s photo shows the layering frozen in time by geologic forces. Considering the angle of tilt, and the camera was level when this photo was taken, it is apparent that an extreme amount of uplift occurred in this area.
Today’s photo was taken at Vasquez Rocks Natural Area Park in northern Los Angeles County with a Canon EF28-135 mm f/3.5-5.6 IS USM lens zoomed to 65 mm on a Canon EOS 5D Mk. The exposure was set at 1/180 sec. at f/8.0 and ISO 400.