Splendid Grand Canyon The rocks in the Grand Canyon area of the United States are mostly red. The exposed layers from the bottom to the top are relatively complete, including the pre-Cambrian, Paleozoic, Mesozoic, and Cenozoic eras. The oldest layer is metamorphic rock from the Precambrian era. The exposed layers are clear in sequence, with different colors, and contain representative fossil specimens from various geological ages. It is also known as the "living geological history textbook".