Nonconformity, Grand Canyon, Arizona. Nonconformities are types of unconformities in which
sedimentary rock depositionally overlies metamorphic or intrusive igneous rock. In this photo, Cambrian
Tapeats sandstone overlies Proterozoic schist, with an age greater than 1.7 Ga--which means that the
erosional surface between the two represents more than a billion years of geologic time! Elsewhere in the
Grand Canyon, the Tapeats Sandstone overlies tilted Proterozoic sedimentary rock to form an
Angular Unconformity.