Buttress Unconformity at Roosevelt Dam, in Maricopa County east of Phoenix. From AGS Field Trip Guide Nov 18, 2000: A 90-foot-deep channel was incised into Troy Quartzite, Mescal Limestone, and basalt. The channel fill includes a ferruginous sandstone, overlain by very poorly sorted feldspathic sandstone.
Buttess Unconformity near Roosevelt Dam, Arizona. Courtesy of the Arizona Geological Society, you can download the guidebook here: http://archives.arizonageologicalsoc.org/guidebooks/AGS_2000-11_Roosevel...
