The Great Valley began as a forearc basin, a sequence of sedimentary layers lying on oceanic crust between a subducting trench and the edge of the North American continent. The sediments were derived from the erosion of the Ancestral Sierra Nevada, which at the time was a string of volcanoes not unlike the Andes or Cascades of today.
What a fascinating time this was! Huge volcanoes were erupting every few decades, while large rivers were constantly eating away at the mountains. A diverse group of dinosaurs roamed the forests on the flanks of the volcanoes including hadrosaurs (duckbilled dinosaurs). Raptors and carnivores similar to T-rex and Deinonychus (the American version of the velociraptors) lurked in the trees and along the rivers. Various species of Pterosaurs flew overhead.
|The first dinosaur found in California was discovered on this ridge above the landslide.|
|Fall colors in Del Puerto Canyon. Unlike the rest of the country, we believe in enjoying the fall until winter actually begins on the calendar.|
The sediments accumulated to an incredible thickness, more than 25,000 feet. The sediments were later twisted upwards to form the eastern flank of the Coast Ranges. The road in Del Puerto Canyon winds for more than 10 miles through the sandstone, siltstone, and shale that once formed the ocean floor. We were driving up canyon, but deeper down into the crust. We were looking for the Tesla-Ortigalita fault that marks the boundary between the so-called Great Valley Group, and the underlying Coast Range Ophiolite, a slice of oceanic crust.