Erosion

As the ice ages came to a close, the environment became warm and semi-arid. Water levels receded and water erosion decreased. Mass wasting, or slope movement resulted in a widening of the canyon and a steepening of the cliffs. An average 2 debris flows, or the funneling of water-laden masses of soil and rock in stream channels, occurs in the canyon a year. These come from tributaries and form or expand rapids.

Crystal Rapids, Colorado River, Grand Canyon.
</br><a href="http://archive.library.nau.edu/cdm/ref/collection/cpa/id/13654" target="_blank">Margaret Eiseman Collection NAU.PH.2004.8.2.42.1</a>
Crystal Rapids, Colorado River, Grand Canyon.
Margaret Eiseman Collection NAU.PH.2004.8.2.42.1