Annotated geology of Red Canyon upstream of mega-landslide in Grand Canyon Supergroup by Brian Gootee. Landslide is on left side of picture and slid to the east (right) some time during the Pleistocene (last 2.8 million years). From Brian Gootee's observations, 'I think it blocked Red Canyon, piled up alluvial fans on the back side, then cut through it where there is a boulder (mansion-size boulders) field downstream of landslide toe. As far as I can tell the fan is Pleistocene but soil development is not obvious.'
George Billingsley of the US Geological Survey first identified the landslide.
Landslide theme at the interactive Natural Hazards in Arizona Viewer - http://uagis.maps.arcgis.com/apps/webappviewer/index.html?id=98729f76e46...