The coarse-grained Calville Bay sediments - Pliocene to Pleistocene - border the Arizona shoreline of Lake Mead below the slopes of basalt-capped Fortification Hill. The Fortification Hill plateau is situated at the northwest end of the Black Mountains. The Calville Bay sediments predate and may be synchronous with opening of the Colorado River.
Online Resources from USGS
Felter & others, 2013, Preliminary geologic map of Black Canyon and surrounding region, Nevada and Arizona. Map plate and text. https://pubs.er.usgs.gov/publication/ofr20131267A