Dave Nelson and I went skiing yesterday, up to Rowton and the meadows in the headwaters of Onion Creek. He did quite well. We were blessed by a beautiful day, with two inches of fresh powder on a firm base. Partly cloudy skies dropped finely shaped snowflakes on us while the sun shone.
I saw a bird dive into a hole in the snow up on top of the ridge near Dave's place. It had been dancing.”
[Russell Towle's journal]
Date: Mon, 10 Feb 2003
To: NorthForkTrails
From: Russell Towle
Subject: Giant Gap by way of Canyon Creek
Hi all,
I met Larry Hillberg, who has been gradually cleaning up the mess out on the Stevens Trail, at ten in the morning, and we snuck into the Gold Run Diggings and drove to the head of the Canyon Creek Trail in Potato Ravine. Larry says that there are probably twenty more loads to be carried out from the Stevens Trail site.
This was Larry's first visit to Canyon Creek. We stopped to admire the great tunnel of the Gold Run Ditch & Mining Co. (1873), crossed the bridge, saved the side trail to the Blasted Digger for later, noted Brewer's Rock Cress and Biscuit Root in bloom at Gorge Point, skipped the Six-Inch Trail to the Inner Gorge, but took High Terraces Trail and then the spur up to the Big Waterfall. We saw many California Milkmaids and some Rue Anemone in bloom. The white racing pigeons were not in evidence.
I remember a friend of mine, Ron LaLande, brought a passel of racing pigeons up here in the mid-1970s, and all but one of them were killed by falcons and bird hawks in fairly short order. The one survivor, a female named Jethro, used to fly beside Ron as he rode his little motorcycle miles in to Dutch Flat. Perhaps these pigeons of the Big Waterfall have been discovered by hawks or falcons.
Returning down the spur trail, we dropped down to the Terraces, where the miners who tended the sluice boxes in Canyon Creek in the 1870s had their principal camp, to find a young man camping there. His name is Peter Fortune, and his camp was neat, and a civil engineering textbook has open beside him on the lawn-like terrace. We chatted with him for a while. It developed that he had discovered Canyon Creek on my web site. I mentioned that only that morning I had thought about taking down the Canyon Creek page, since too many people seem to be discovering it. However, young Peter Fortune is just the kind of person I like to see in there. He is a friend of Gene Markley, the famous gorge-scrambler and master of obscure mining trails in the American River basin, and Peter and his friends consult with Gene and then explore accordingly. He has done the Royal Gorge, Giant Gap, the gorge between Euchre Bar and Green Valley, and other parts of the North Fork. In fact, it was Peter who did the trail work Catherine and Ron Gould and I observed in the east end of Green Valley, a few weeks ago.
Peter mentioned what I had also recently heard from Ron, that the side trail to Green Valley from the Euchre Bar Trail has been flagged in red; Peter adds that the flagging extends to the summit of East Knoll. This worries me, as a private parcel extends to the top of East Knoll from the river, and I have heard the inquiries were made to Tahoe National Forest by someone owning property in Green Valley, who wished to bulldoze a road down there. TNF made some efforts a few years ago to purchase the private inholdings in Green Valley but failed.
Larry and I left Peter to his studies, and took Lower Terraces Trail back to the main trail and quickly reached the river. The day was surpassingly sunny and clear. After a short break, we decided to explore the upriver trail. This trail passes a rather nasty cliff only a couple hundred yards east of Canyon Creek. From this first part of the upriver trail one can see, alternately, the Pinnacles on the right, and Lovers Leap on the left, as one looks up into Giant Gap.
Here one reaches a gully and a problematic part of the upriver trail. East of the gully is a difficult patch of brush with much thorny Buckbrush. At the lower level, around one hundred feet above the river, where we hit the gully, there is no clearly-defined continuation of the trail. At higher and then still higher levels, there are two trails leading out of the gully to the east, but both enter the brush-patch, which is nearly impassable. Larry and I just stayed low until past the brush and then switched back and forth up grassy slopes between rock crags until we reached the upriver trail again, here around three or four hundred feet above the river.
This trail probably dates back to the Gold Rush, and then likely was used by Chinese miners working the river in the later 1850s and 1860s. Wherever the canyon narrows into a gorge it is forced to follow a higher line. It was very open and sunny and we saw Houndstongue in full bloom.
Now nearly a mile upstream from Canyon Creek, and so high above the river, we enjoyed very fine views of the remarkable cliffs and pinnacles of Giant Gap. In places we lost the trail, but always rediscovered it, and finally it descended back to river level, at a sharp bend in the river.
The sun was lowering as we began our retreat back down the trail. When we reached the Brush Patch near the gully, we did some crawling and found the higher of the two trail lines into the gully. Since we were fully 400 feet above the river, and since we agreed that elevation is a precious thing, we decided to angle up and to the west and strike the ridge dividing Canyon Creek from the North Fork at the Blasted Digger Overlook. This turned out to be somewhat harder than we had imagined, but it was interesting to be on such wild cliffy slopes. There are a couple of gullies which contain great fields of angular talus.As we slowly zigged and zagged up and to the west past crag and shrub a falcon zoomed by, heading west. It had a lot of white on its head, and I am not sure what species it was.
Finally we gained the ridge, only a hundred yards from the Blasted Digger. I had hoped to stop and rest there and enjoy the fine view, but the sun had set for that point, though still gilding the high cliffs across the canyon, and a chill was in the air. We took the trail back to Canyon Creek and arrived at Potato Ravine in another fifteen or twenty minutes, very tired and scratched, but pleased to have visited such an inaccessible and beautiful part of the canyon.
Such was a day on the North Fork American.
Cheers,
Russell Towle
Thrusting Shoo Fly
[North Fork Trails blogpost, February 10, 2008:On YouTube, at
http://northforktrails.blogspot.com/2008/02/thrusting-shoo-fly.html ]
http://www.youtube.com/watch?v=J3KryrAGkBo
is an animation of a flight up the American River Canyon, using the USGS Digital Elevation Model 30-meter data set, and merging a couple dozen DEM quadrangles to build a landscape spanning Colfax on the west, the Sierra Crest on the east, the San Juan Ridge and Grouse Ridge to the north, and the Middle Fork of the American on the south. The virtual camera follows an almost due east heading from west of Rollins Lake, crossing over Lovers Leap and Green Valley, and flying on up the canyon into the Royal Gorge. The animation finishes with the virtual camera making an orbit of 360 degrees around Snow Mountain.
Thrusting Shoo Fly: on my iMac I can set the screensaver to loop through any folder of images in my iPhoto library. It so happens that right now it loops through a folder of some of my favorite photographs in the North Fork. Here is Giant Gap, from the west, and now from the east; or the 500-foot waterfall in New York Canyon, or Big Valley Bluff at dawn, as seen from the North Fork, a couple miles up the canyon.
And so on. It's not hard to take beautiful photographs in such a beautiful place.
It happens that one of these special photographs shows what I call Bluff Camp, an old mining camp immediately adjacent to the river, set on a cliff-bounded strath terrace bearing a fine grove of Canyon Live Oaks. From the North Fork American River Trail, connecting Sailor Canyon to Mumford Bar, a side trail leads one down a hundred yards, or so, to Bluff Camp. I have camped there many a time. It is half a mile or so east of Tadpole Canyon, and directly below Big Valley Bluff, rising in ragged cliffs all of 3500', across the river to the north.
And the photograph was taken from a point upstream from Bluff Camp; so one sees a part of the encircling cliffs, and a flat area—the strath terrace—perhaps thirty feet above river level. (A "strath terrace" is a glacio-fluvial landform associated with glacial outwash sediments which once occupied the terrace itself; and it was these very sediments which planed down the bedrock, to make the terrace).
It caught my eye, the other day, the Bluff Camp photo, as it filled the screen; I could see an abrupt change in the bedrock, right at the upstream end of the strath terrace. Slowly, dimly, I realized I was seeing a thrust fault. Two disparate bodies of rock had been juxtaposed by faulting.
The bedrock for miles up and down the canyon is composed of metasediments of the early-Paleozoic "Shoo Fly Complex," the oldest rocks in all the Sierra. I have a wonderfully precise geologic map of this part of the North Fork canyon, made by David S. Harwood et. al. of the USGS, in the early 1990s. Harwood shows many thrust faults in the Shoo Fly Complex near Big Valley Bluff, Sugar Pine Point, and New York Canyon. The faults sometimes bring big blocks of chert, hundreds of yards in extent, or more, into contact with slates and other types of rock in the Shoo Fly Complex.
By the way, it is called a "Complex" because it is composed of many distinct formations, spanning many millions of years in time, but all very old. Harwood describes and names four such formations in this particular area. His map does not show the Bluff Camp Thrust, which is probably a sensible choice, for it is likely not very long or large as thrust faults go, and if he were to put every such minor thrust fault on his map, well, there would be room for precious little else.
It has long been considered that the great mashing-together, the epochal juxtaposition of the disparate Sierran metamorphic rocks alongside one another, took place around 145 million years ago, in what was named the "Nevadan Orogeny" (an "orogeny" is a mountain-building). It was this Nevadan Orogeny which acted to rotate all these disparate bodies of metamorphic rock almost 90 degrees to the east, so that what were once flat-lying beds are now almost vertical, or even slightly overturned. And it is considered that the "penetrative fabric" of these disparate metamorphic rocks is mainly due to the Nevadan Orogeny. The compressive and shearing forces which imparted the fabric were fairly well parallel with the current, almost-vertical orientation of the beds. Very likely it all had to do with continental accretion, at a time when Pacific ocean floor was being actively subducted beneath the continental margin, moving from west to east, but also plunging steeply down.
However, in many of these different metamorphic rock formations, whether they be down by Auburn or up at Big Valley Bluff, an experienced eye can detect at least two different episodes of deformation, each leaving its footprint, or imposing its fabric, upon the rocks. There is the later Nevadan Orogeny; and at Bluff Camp, there is a thrust fault vastly older than the Nevadan Orogeny. That is to say, the Shoo Fly was already well-deformed, well-sliced and diced by thrust faults, long before the Nevadan Orogeny.
And Harwood discusses all this in the twelve-page essay which accompanies his map. There are a couple of typographical errors in this essay which play the very devil in understanding the thing.
It is not at all easy to learn to recognize these different rock types. That this is chert, and that is quartzite, may not be discernible except under a microscope. To develop a simple portrait of the bedrock geology, one can read what was written about it a century and more ago. At that time the focus was upon the broad outlines, not the higgley-piggley details. And for a time, the following usage had currency, for instance, in the articles by C.J. Brown of Dutch Flat, published in the Mining & Scientific Press, in 1875.
Brown divides the metamorphic rocks as follows: the Western Slate, the Middle Slate, and the Eastern Slate. Between the Middle Slate and the Eastern Slate, he identifies the long narrow serpentine belt we now name for its associated Melones Fault Zone.
Hence his Eastern Slate corresponds to the Shoo Fly Complex, and those other Paleozoic and Mesozoic rocks which lie on top of the Shoo Fly, and therefore, to the east (the whole shebang, be it remembered, rotating 90 degrees to the east during the Nevadan Orogeny).
Brown's Middle Slate corresponds to the Calaveras Complex, another complex of formations, but late-Paleozoic in age, and he correctly identifies the rock of Giant Gap as metavolcanic—in fact, Brown declares it to be metabasalt; and his Western Slate corresponds to all those metamorphic rocks west of Cape Horn, in which there are several distinct formations, often dominated by metavolcanic rock, but containing some metasediments, too.
So, if we wish to blur our focus and appreciate the broader outlines of local bedrock geology, we might give C.J. Brown's Western/Middle/Serpentine/Eastern model a try.
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