Geo Lab - Pillow Basalts Traditional Cache

This cache is a camo'd, small lock and lock located along the Headlands Trail in Andrew Molera State Park. The trail is relatively flat with a few wooden stairs here and there. There's no need to climb down from the bluff to find the cache, but if you do make sure to check out the awesome garnet sands!

Recently, I took an introductory geology class and learned much about the geologic history of the Monterey Peninsula. My goal is to eventually expand this into a nice and short series that I hope will help educate and appreciate our beautiful local environment. This cache is located at a very unique spot along our coastline.

Just below the cache site sits some pillow basalts. What's so rare about pillow basalts? Well, pillow basalts form in deep sea basins at a divergent plate boundary. At these locations, magma seeps from cracks in the Earth's crust and is quickly cooled by the ocean water, creating the pillow-like, fluffy appearance. Along these divergent boundaries, large mid ocean ridges form mountain chains much longer than anything we see on the Earth's surface. As the magma continues to seep, the sea floor continues to spread. Eventually, the crust meets the continental shelf, subducts, and forms a deep sea trench. As oceanic crust is much denser than continental crust, most pillow basalts are destroyed as the oceanic plate dives kilometers below the Earth's surface.

The pillow basalts at this location are a remnant of an ancient subduction zone which helped form the Sierra Nevadas. As the oceanic crust subducts, some of the material gets scraped up and is left on the surface. This is just one of two sites along the California coast where you can see these rocks. Enjoy your time at the cache, and imagine just what this coast looked like millions of years ago.