Thursday, May 31, 2012

Cronks Canyon

The photo of the paddler in the website cover graphic is the Editor's wife, Susun McCulla, in front of our AIRE Lynx II as we approach the head of Cronks Canyon.

Last May 31, in honor of this now ubiquitous profile photo, we thought we would take time to talk a little bit about the intriguing area of Cronks Canyon, also known as The Royal Gorge of Idaho.  While that's a tad bit of hyperbole, some folks think the label fits.  In our opinion it's little too short, shallow and small to receive such the grandiose title of a Royal Gorge.

The canyon is named for James Cronk, an early day cattleman who ranched in the area.  Many local creeks, rocks, canyons and other places received their enduring names from whoever settled or ranched there first. Such was the case with Cronks Canyon.

As everyone knows, the geology of The Upper Salmon River covers a lot of bases.  The majority of the upper river's ramparts are mostly volcanic in origin and many a story can be told or invented about the "where, when, why and how" of those rocks' origin.

Cronks Canyon is not strictly volcanic in origin--its composed of a Precambrian sedimentary deposit that was metamorphosed into the formation now known as the Swauger Quartzite.   This formation is most likely from 850,000,000 to 1.5-billion years old.  The Swauger and its Precambrian cousins make up a large chunk of the Lemhi Range.  The rock unit was named for the first place it was studied back in 1947 on the Swauger Ranch near the watershed divide between the Pahsimeroi and the Little Lost Rivers.  Cronks Canyon provides one of the better and easily accessible glimpses of this rock unit. The Swauger Quartzite displays a wide variety of colors including light gray, pale to dark blue green, pale red purple, pink and pale orange.

Perhaps that's one reason an anonymous author for the Federal Writer's Project wrote in 1937, " is here that the most beautiful coloring is to be seen.  The rugged bluffs here standing as walls against the highway are stratified in red and yellow, green and dark blue, and even under the morning sun are extremely rich.  At sunset, when burning evening streams up this forge, this mountainside in its bewildering loveliness looks as if a thousand broken rainbows had been drawn into the stone."

Respected Custer County geologist Falma Moye wrote in 1990, "The Salmon River has been superimposed and cut a narrow channel through the quartzite.  Notice that the river follows planes of weakness, both bedding and fractures in the rock."

Cronks Canyon is a fun little ride at all water levels.  At high flows it washes out.  The most fun to be had comes in July and August when some of the rocks are nearly exposed and enjoyable maneuvering can be had.

Here are some Google Earth screen clips of Cronks Canyon.  A YouTube fly-through is below.
Above is a Google Earth view looking downriver toward Cronks Canyon.  
That prominent rampart on the left is mostly pure Swauger Quartzite.
The red "X" shows Cronks Canyon in relationship to the area where the Swauger Quartzite was first investigated and described in 1947 up on the Swauger Ranch at the head of The Pahsimeroi. (Red "Y".)
There an interesting close cousin of The Swauger Quartzite (A) located upstream at point B just downriver from the confluence of The Pahsimeroi.  According to Geologist Falma Moye,  "This (Apple Creek Formation) is mainly siltstone and fine-grained sandstone.  The rocks breaks easily along bedding layers because those surfaces are coated with mica.  This is a good place to look at features which formed during sedimentation.  In particular, there are some good examples of ripplemarks and there are also examples of cross beds and channels. In addition to primary sedimentation structures this rock also shows the effects of deformation."
Above is one of our first attempts to experiment in converting a Google Earth fly-through into a YouTube video with audio descriptive dubbing.

No comments: