what kind of rock is in joshua tree
Joshua Tree National Park The park's oldest rocks, Pinto gneiss among them, are 1.7 billion years old. They are exposed in places on the park's surface in the Cottonwood, Pinto, and Eagle mountains. Much later, from 250 to 75 million years ago, tectonic plate movements forced volcanic material toward the surface at this location and formed granites, including monzogranite common to the Wonderland of Rocks, parts of the Pinto, Eagle, and Coxcomb mountains, and elsewhere. Erosion eventually exposed the harder rocks, gneiss and granite, in the uplands and reduced the softer rocks to debris that filled the canyons and basins between the ranges. The debris, moved by gravity and water, formed alluvial fans at the mouths of canyons as well as bajadas where the alluvial fans overlapped.[22]