In last week’s Science Wednesday, I covered the geology that created the Gulf of California and Baja California. This week, I want to share some photos from a particular island in the region: Isla San Jose, home to some stunning geology, particularly at a place called Punta Colorada. Along one section of the island there is an outcropping of bedded sandstones a few hundred meters thick that date back to the Late Pliocene, a few million years ago, embedded with potentially millions of seashells. Geologically speaking, this is quite young! When walking amongst the landscape, seeing shells on the ground and along the walls, they looked as if you could just pick them right up, but, when you tried, you’d soon find out that they were embedded in stone!
Sandstone is a sedimentary rock – basically, compacted sand made up of common minerals like quartz and feldspar. Layers of sand can build up as sediment either underwater (like in this case) or on land, like in deserts. As the sand particles get compacted by pressure of overlying deposits, they get cemented, or, naturally ‘glued’ together. For sandstones that have a reddish hue to them, this typically signifies the presence of a mineral called iron oxide as well. The reason these sandstones are at the surface now ties back to the tectonic history of the area – uplift brought up the rocks, above sea level, after all the time they spent underwater, collecting shells and stones. While erosion due to wind and water can soon destroy these types of features, this particularly region doesn’t see much moisture. The erosional effects that can be seen are the formation of voids or cavities due to the physical force of the wind and the chemical action of the salt from the sea. There is a lot to explore in Baja California – a true gem of a place on this planet!