Joshua Tree National Park in California is famous for its namesake Joshua Trees (Yucca brevifolia), and its amazing geology. The geology is largely composed to two distinct rock formations that were created about a billion years apart in time. The backbone of the mountain ranges in the park is Pinto Gneiss (pronounced "nice") that was formed about a billion years ago when ancient offshore sedimentary rocks were thrust up by the collisions of unknown continents in the formation of the super-continent Rodinia. Gneiss is a metamorphic rock formed when extreme heat and pressure is applied to sedimentary rock. This rock can be seen today in the jagged, broken mountains surrounding Indian Cove campground and the western entrance to the park near the town of Joshua Tree.
The other major, and probably more famous, rock formation found in the park was formed during the break-up of Pangaea, the super-continent that formed about 280 million years ago when, after the break-up of Rodinia, the Earth's continents came together once more. As Pangaea rifted apart, the section that was to become modern day North America drifted west, colliding with the tectonic plate underlying the newly forming Pacific Ocean. The Pacific Plate, being less dense than the continental rock of the North American Plate, sank below it, back into the Earth's mantle. As the Pacific Plate sank below the North American Plate tremendous friction created intense heat which melted rock into liquid form. This molten rock, being less dense than the North American Plate began to work its way up through faults and crack in the continental crust, eventually cooling and solidifying beneath the surface of western edge of the continent.
Erosion by water and wind eventually stripped the softer material that lay above this cooled mass, exposing it to the atmosphere, where these elements continued to sculpt it into the bizarre shapes we see today. Classified as monzogranite by geologists, these formations are the end product of the intrusion of hot magma into the Earth's crust below what is the Mojave Desert in modern day California in North America.
This week's photo was taken with a Canon EF 100mm f/2.8 Macro lens attached to a Canon EOS 5D Mk III. Exposure was set to 1/500 sec at f/11 and ISO 1600.