The following is a transcript of the narration for this panorama location. To watch and listen to the narrated panorama, enter the project here at this location and then press the play button.
We have now descended about half way down to the Colorado River from the Tapeats Sandstone rim of the inner canyon. We are surrounded by the dark Vishnu Schist that dominates the rock of the inner canyon, and the temples and buttes of the upper canyon are disappearing. Isis, Buddha, Sumner Butte, Zoroaster, and Bradley Point are still here, but soon most of them will disappear as well as we descend.
We are again, just like we were up above at Panorama Point, standing right at the boundary between the Hakatai Shale and the Bass Formation. If, however, we look back in the compass direction of Panorama Point, we see nothing but Vishnu Schist level with us, but panning up to the point we do again see the Hakatai / Bass boundary, but now far above us. And if we look around the entire scene more carefully, we can see other pockets of Hakatai and Bass. Here, downstream on the north side of the river we see a splotch of Hakatai – the same splotch we spotted from much higher up on the South Kaibab Trail, and here, another isolated splotch on the far side of Bright Angel Canyon in the direction of Buddha Temple. Around here, below the Tapeats Sandstone and the Great Unconformity, the geology is a mess.
Look at the USGS geological map for the area and you can see why. Our location is at the position of the orange dot, and there are faults all over the place. But why so many faults right here? Geologists have spent decades attempting to reconstruct the history of continental drift, determining just where the continents were and when over billions of years. And they currently believe that one billion years ago most of the land masses of planet earth were jammed together to form a single supercontinent named Rodinia, and here’s a map of one guess of what it looked like. The land mass named Laurentia on the map included the Grand Canyon area, and most of what is North America today. Supercontinents, however, are not stable – sooner or later the same forces deep within the earth that drive continental drift will rip them apart.
Rodinia’s time to be ripped apart arrived 750 million years ago. A rift formed a few hundred miles west of the Grand Canyon area, somewhere around where Death Valley is located in California today. The portion to the east became what is North America today, and what drifted off to the west was, depending on which geologist you talk to, either Antarctica or Australia. For hundreds of miles from the rift, including the Grand Canyon Area, large faults like the Bright Angel Fault sliced up the land, and in some places, like here, numerous smaller faults radiated out and parceled up the area even more.
Right here we are standing inside the Cremation Graben. Graben is a German word that means grave. The Hakatai Shale and Bass Limestone layers we stand on were laid down as sedimentary layers on top of the Vishnu about a billion years ago, but here, in the grave, they have been lowered down into the ground beneath the surrounding Vishnu, filling up part of the space forming between the separating continents. Look off to the southeast, and you can see the Cremation Fault, the eastern boundary of the Cremation Graben. Vishnu Schist is to the left, and the Bass, Hakatai, and Shinumo Quartzite formations, originally laid down in layers on top of the Vishnu, are to its right.
Another fault, the Tipoff Fault, marks the western boundary of the graben, but we can’t see it from here. Instead we see yet another, unnamed fault line that cuts through the middle of the graben and dropped this spot even further beneath the already lowered Bass and Hakatai rocks we see back up at Panorama Point.
But by 545 million years ago the ground was quiet. The area of the Grand Canyon was a flat plain with just a few hills poking above the shallow sea that laid down the Tapeats Sandstone, burying the story of a doomed supercontinent, told by the rocks below the Great Unconformity, until the carving of the Grand Canyon revealed it for us to see today.
Heading up the trail from here, we switchback up through the Hakatai Shale within the graben to Panorama Point, for a beautiful panoramic view of the river, including both the Black Bridge and the Silver Bridge.
Heading down the trial, we soon leave the Hakatai and Bass for good, down to a panorama point near the junction of the South Kaibab and River trails, with a fine view of the Black Bridge from just above.