Thinnly laminated, Pliocene Bouse marl at Silver Creek (near Oatman), Black Mountains, Mohave County, Arizona. Inundation was geologically brief – the underlying alluvial fan conglomerate was submerged, silty limestone was deposited, and then standing water receded and alluvial-fan deposition resumed. The contact between Bouse marl (lower) and the capping alluvial fan deposit is razor-thin.
See Jon Spencer's, Arizona Geology article, "4.8 Ma Age for Inception of the Modern Colorado River" for more on the Bouse Formation.
http://azgeology.azgs.arizona.edu/article/feature-article/2011/12/48-ma…
Photographer: Jon Spencer
Photo Date: circa 2010