Exploring how the Grand Canyon ends

draft - EXPLORING HOW THE GRAND CANYON ENDS - draft

From the Westernmost High Point, the view sweeps down and out, over the Sanup Plateau, reaching its farther edge some seven miles west where it drops 3500' in 1 1/2 - 2 miles to the water surface (of the reservoir or river, depending). That drop is a geological lesson, as shown in this piece of the 1982 edition of the stupendous, irreplaceable map done in the 1970's by Peter Huntoon and George Billingsley. (For orientation, keep track of that triangular flat in the middle at the top.)

From high up, the googleview emphasizes the drainages running from the Sanup (that triangle) to the river:

The geology in color, from the WHP (sitting in the aqua of the Hermit shale) on the right across the light blue Sanup down to the river, and over it onto the light green rocks whose youth at this end constrains the Canyon's age, showing it as a young feature:

Then the USGS quad titled Snap Canyon West:

The pencilled-in lines are along ridges delineating the last two side drainages into the Colorado before we reach the buttes of the west exit (at 3). Beyond the northern line the drainage is into Pearce Canyon, and much of that surface is the Muddy Creek Formation (Billingsley/Huntoon) or "Rocks of the Grand Wash Trough, paleozoic-clast conglomerate", green on the color map above. The layers southeast of the green are Grand Canyon, especially the limestones below the Supai and prominent in the west: Redwall, Temple Butte, Muav, and down to some Bright Angel, with landsliding, travertine, and silt & gravel from  reservoir action. My point being that this west ending is the Grand Canyon geology saying goodbye.

Back up, then, to an overall orientation: The Westernmost High Point is on the extreme right (that dragon head). Go west from its nose across the Sanup in a shallow curve to the edge, --note that triangle--, down to the river and around the bend from north-going to west, where the darker west exit buttes sit -- Paiute on the north, Hualapai on the south.

Pearce Canyon runs across the top third; to its east, the curving cliff of Snap Point, the current anchor of Grand Canyon National Park. 

And this is where we, determined to enlarge the Park as much as we could to match the Canyon itself, confused matters, for the Park contains land that is not in the Canyon's defining drainage -- Pearce and Snap for instance drain due west into Lake Mead. And south across the river that sharp ridge in the map above paralleling the river marks the Grand Wash Cliff line that is the Canyon's western boundary. However, we were not careful, and so took into the Park flatter land to the west that drains away from the Canyon itself.

So much for history...here is a little fillip for the tour's end: Go back up to the top map (Billingsley-Huntoon) for an oddity: right in its center is a feature that should be on any west end tour-trek: the Grand Pipe. (Yes, sadly it drains into Pearce.) A breccia pipe collapsed top, you can find it in maps below. On the colored geology, it shows as Hermit shale, though it is actually lower by 100'-200' than the surrounding Supai formation of the Sanup. And a short walk west to the Sanup rim and a view down over the jumbled washes tumbling to the river; the topo map showing the three routes down along dividing ridges.

Enjoy your walk!