In this photo I am standing in a graben and looking at a graben. Bass, Hakatai and Shinumo rocks managed drop down during rifting from tectonic movements during the breakup of supercontinent Rodinia, evading full erosion.
I am standing amidst the Shinumo rocks a short way down South Kaibab trail from the Tip Off Rest Area. The Colorado is too deep to be seen from this angle but it passes a bit below the greenery marked ‘BA Camp’ (Bright Angel Campground).
Note: This is my best current interpretation. The labels for Rama Schist and the granitic rocks may be off a little, so no arrows. I marked ‘The Train Wreck’ rock as Tapeats, but it’s not entirely Tapeats, and I have not, as yet, gotten that far. I am fairly certain that I’ve gotten the Bass cliff labels right but where there is a Bass slope it’s hard for me to distinguish from Hakatai slope and basement rock slope. Granitic Xgr is not a real rock name, but short for a rock unit called ‘Granite, granitic pegmatite and aplite’ in the mapping sources listed below, more commonly referred to as Zoroaster Granite.
Sources used:
Billingsley, G.H. 2000. Geologic Map of the Grand Canyon 30′ x 60′ Quadrangle, Coconino and Mohave Counties, Northwestern Arizona. U.S. Geological Survey. Geologic Investigations Series I-2688, version 1.0. https://pubs.usgs.gov/imap/i-2688/.
Clark, R. 2013 (work in progress). Geology of the Grand Canyon interactive map. Geology mapped by George Billingsley and others at the U.S. Geological Survey. Arizona Geological Survey. https://rclark.github.io/grand-canyon-geology/.
Google Earth Geologic Resources Inventory Project for Grand Canyon National Park. 2001-2013 https://irma.nps.gov/DataStore/Reference/Profile/2203634.
Ranney, Wayne. “Making Sense of the Supergroup”. National Parks Service. Presented October 13, 2020 at Virtual Grand Canyon GeoFest 2020 – Day 3 – minute 4:33. https://www.nps.gov/grca/planyourvisit/virtual-grand-canyon-geofest-2020.htm or https://www.youtube.com/watch?v=BzkgjyIJpmU.
RocksTalk 