Over 115 million years ago during the Cretaceous period, plate tectonics forced the Pacific plate to slide under the North American plate. Heat and pressure from movement 25 miles deep formed Metamorphic rock called Catalina Schist. Over millions of years of uplift and erosion, this Catalina Schist rose near the surface of the earth.
About 16 million years ago sea beds were deposited on top of this Catalina Schist. These sea beds continued to be deposited for about 2 million more years. These beds, now over 1,000 feet thick, are called the Altamira shale or Palos Verdes Stone. As layers of this Altamira were being deposited, volcanic basalt was being injected into these beds below the sea floor. These are called basaltic dikes. In some spots the basalt would break through the sea floor into the cold ocean forming pillow basalt. These can be seen in the Livingston Quarry (located in the Forestal Nature Preserve). Because of movements in the San Andreas Fault, all this activity 14 to 16 million years ago actually took place in deep water off Mexico’s Baja Peninsula.
Altamira Shale or Palos Verdes Stone was formed during the Miocene epoch. Life in the Miocene seas of Palos Verdes was much like life today in the Catalina channel, deep water 3,000 feet deep and having rivers flowing into it. Fossil fish, fish scales and whale bones are commonly found on the Peninsula, and many are from the families still living in the Pacific today. A few exceptions would be the fact that Miocene whales were much smaller than the ones living today. Specimens 20 feet long would be the maximum size for a fossil whale in Palos Verdes. Sharks on the other hand evolved in the other direction. The giant Mako on display at the Point Vicente Interpretive Center could reach 20 feet in length (modern Mako sharks reach up to 13 feet). The top predator of the Miocene seas was the 50-foot long Megalodon shark. A tooth from this monster was found at Pelican Cove below the Point Vicente Lighthouse and was nearly six inches long.
Today most of the rocks found on the Palos Verdes hills are from the Altamira shale. Because of the color and beauty of these rocks, they were commercially mined under the name of “Palos Verdes Stone”. Local decorative walls, patios and even the exterior walls of the Point Vicente Interpretive Center are covered with Palos Verdes Stone.
After the Miocene beds were formed 14 to 16 million years ago, nothing geologically speaking happened until about 1 million years ago. At this time because of pressures forming beneath the earth’s crust, these sea beds began to push up. The Catalina Schist covered with the Altamira Shale was pushed up through the ocean, breaking the surface and forming a small island. As Palos Verdes Island continued to rise out of the sea, it formed sea cliffs around its perimeter. Today these old sea cliffs or marine terraces can be seen on the hillsides. Thirteen of these Pleistocene epoch marine terraces were formed over thousands of years. At the base of these ancient sea cliffs in some areas you can find fossil seashells and the remains of tide pools. Most of these fossil shells are the same species as the ones found in our local tide pools today.
Your artickle is such an exciting, almost visual, depiction of our geological history. Thank you.