Question: what kind of rock is in joshua tree

title: Joshua Tree National Park
text: 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 . 

Answer: answer: The park 's oldest rocks , Pinto gneiss, are in Joshua Tree National Park. 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 .