Monday, September 9, 2013

Into the Great Unknown: A Gigantic Failure Produces One of the Most Beautiful Sights in the Grand Canyon

We continued down the Colorado River, the "Great Unknown" as it was called by John Wesley Powell during the first boat trip through the Grand Canyon in 1869. In the last post, I mentioned that we passed through the narrowest channel in the entire canyon, a spot in the Granite Narrows where the river is 76 feet across and more than 100 feet deep. I didn't mention why this spot just happened to be so narrow. The story of how it got this way touches on our next pull-out at Deer Canyon Falls, and on Yosemite Falls in a totally different national park back in my home state.
In my youth, I used to drive up San Antonio Canyon in the San Gabriel Mountains, and my poor little VW Bug had trouble surmounting a big ridge called the Hogback. It was a gigantic rockslide that had forced the creek into the cliff, where the river was forced to erode a granite slot canyon in an otherwise debris-filled floodplain.
I found out that the narrowest channel in the Grand Canyon formed in much the same way! It turns out that if you stack thousands of feet of sediments onto a plain that then rises to become a plateau, and carve a deep canyon into it, it will turn out that some layers will fail due to the weakness of the rock and form gigantic rotational slides. At Granite Narrows these large rotated blocks blocked the flow of the Colorado, forming a temporary dam and causing the river to establish a new channel in the hard rocks of the Granite Gorge Metamorphic Suite. Because the channel is newer, it has not had time to widen as much as older parts of the canyon.
The picture above shows the Granite Narrows from the vicinity of Deer Creek Falls, with a portion of the Surprise Valley slide on the left side above the river. It also turns out that the landslides in the area had another unexpected result.
Deer Creek Falls sits at or near the top of a list of the most beautiful sights along the Colorado River in the Grand Canyon. The creek seems to burst out of the canyon wall, falling a hundred feet or so onto the river shore (during periods of highest flooding, the waterfall tumbles directly into the Colorado). It was truly a stunning sight as it became visible around a turn in the river. We pulled out to have a closer look.
We took the very steep and hot trail that climbed out of the Granite Gorge and into the Tapeats Sandstone where Deer Creek has carved what may be the most incredible narrows in Grand Canyon.
The trail clings to a ledge midway up the cliff in the narrows, and it includes a couple of hair-raising steps around protruding rocks (it's on the right side in the picture below). A slip here would incur a very uncomfortable drop of 50 feet or more.
As you make your way up the gorge, it begins to dawn on you that this canyon is very narrow compared to others in the Inner Canyon, despite the rather high permanent flow of Deer Creek (the creek is fed by a large spring complex just upstream). A relatively large stream like Deer Creek ought to have been able to erode a much wider canyon. Even stranger is the relative lack of erosion at the falls. Shouldn't a stream like Deer Creek be able to erode at least some of the way through the hard metamorphic rocks? Literally every other tributary canyon has managed to do so.
The narrows are just gorgeous. I had seen a picture of them in a book when I was a teenager, and I had been wishing to hike them in real life for a long time. I was in a sort of walking dream just being there.
We could hear the water pouring through the canyon below us, but it took awhile before we could actually see it. 
The canyon started to open up a bit, and we could see cottonwood trees upstream. We were reaching the top of the Tapeats Sandstone and the lower reaches of the Bright Angel Shale.
 The creek was at trail level. Soaking and splashing time! It was a hot day and a hot hike...
I later came to realize what should have been obvious. The narrows were there because Deer Creek was younger than the other tributaries along the Colorado. Deer Creek Falls are there for the same reason. The canyon hasn't existed as long as the others. But why?

It boils down to the same reason that the canyon is so narrow just upstream. Landslides (slope failures) filled the ancestral Deer Creek Canyon, forcing the stream into a new channel. The diversion happened recently enough that the creek has only carved through the relatively soft Tapeats Sandstone, and hasn't really begun carving into the harder metamorphic rocks.
So it turns out that one of the most beautiful places in the Grand Canyon was the result of failure. A giant slope failure. Mass wasting, a term that encompasses all of the different kinds of slope failures and landslides, was a main tool in the carving of the Grand Canyon. The Colorado River cut downwards, while mass wasting widened the gorge, as it is still doing today.
What does this have to do with Yosemite Falls out in California? Like Deer Creek Falls, Yosemite Falls looks too "young". Yosemite Creek has not carved much of a channel at the top of the falls, which spill over a 1,425 foot high vertical cliff. It turns out that the present day falls are young, too, the result of an Ice Age glacier that diverted and blocked the old Yosemite Creek channel. You can see the older channel to the left of the modern-day falls in the picture below. It is the route of the Yosemite Falls trail today.

After our incredible journey through the narrows of Deer Creek, we got back on the river and rode through Doris Rapid. Although only rated class 3, it was the splashiest ride in a few days. We set up camp at the base of the rapid. Under a steep overhanging cliff...
Lava Falls Rapid was two days away....


Celia Lewis said...

Wow - what a wonderful day! So much to examine and enjoy. Thanks so much for the information and photos.

Gaelyn said...

I am so glad you stopped here. We ran out of time. Amazing slot!

intaminag said...

It's those cool little tidbits about Yosemite falls that make your blog even more worth the read! As if I needed an excuse. :)

intaminag said...

It's those cool little tidbits about Yosemite falls that make your blog even more worth the read! As if I needed an excuse. :)