October 20 (1976, 2002)
Torreya Cliff in Giant Gap Ravine

10/20/76 ~ before dawn, canyonland. interesting how in this reflected, scattered light the giant gap spur stands out well-defined from the canyon wall. after dawn and the entry of direct light into the canyon, the spur seems to collapse back into the shadows and one hardly sees it there.

asleep early, awake early. the stars were still out when i fired up my stove to make my coffee. high cirrus clouds can now be seen around the horizon, and they can only mean a weather front approaches ~ the possibility of rain within a day or two… today will indeed be the day of the saw for me ~ many rafter ends to trim (i let them run wild) and pieces of blocking to cut. if all goes well i should drive down to the coast and back with a load of 2x6 T&G on willy. poor willy, whose battery no longer charges and must be push-started every time. who needs an oil change and a tune-up and some dozens of other things. whose transmission again makes ominous sounds ~ oh please, willy, do not fail me now! but if all goes well, i may have a roof on this cabin by this time next week. hold off, weather, for only another little while please!

[...]

dawn is here with a muted light that speaks of clouds over the sierra crest… well, to breakfast. [...]

~ a couple of hours later, with the teeth of giant gap spur now alight. the rafter ends have now been cut, as well as the ridge pole ends. now all that remains is the blocking ~ horrors! if i use the six-by-six only on walls one, three, four, and six, that means twenty-four sawcuts, four of which are those terrible long compound angles. [...]

glory be! i've cut the last piece of blocking, drove it into place with my splitting maul, and now not another six-by-six need be cut. the roof can go on ~ though I still have a few details...  […]

such a fine day in the canyon ~ the afternoon breeze, beneficent sun warmed me to my fingertips and my toes enjoyed it also. such a beautiful day, much haze in the air, and the oak leaves sailing in the breeze. the giant gap spur is an island of shadow in the afternoon that i always delight in watching. i have no time for backpacking now and even an hour's ramble with neil the other day seemed an extravagance, but i have plenty of natural beauty to keep me satisfied without all the moving around, right where i'm building my cabin.”

[Russell Towle's journal]


Date: Sun, 20 Oct 2002 11:13:06 -0800
To: North_Fork_Trails
From: Russell Towle
Subject: Torreya Cliff in Giant Gap Ravine


Hi all,

For many years now I have wanted to explore Giant Gap Ravine (or "Giant Gap Gulch," as the USGS 7.5 minute Dutch Flat quadrangle would have it). This north-flowing tributary of the North Fork American is one of a matched pair of ravines incised into the serpentine of the Melones Fault Zone in Green Valley, on the south side of the river. Giant Gap Ravine is the more westerly, McIntyre Ravine, the more easterly. Both ravines are somewhat less than two miles long. Giant Gap Ravine debouches into the North Fork near the Gold Ring Mine. The upper ends of both ravines are partly encircled by ridges capped with the "young volcanics," rhyolite ash and andesitic mudflow of the Valley Springs and Mehrten formations, respectively. The ridge between the two ravines hosts the southern reach of the Green Valley Trail, and is almost entirely on Tahoe National Forest lands.

This year I decided I could not put it off any longer. I wanted in particular to see if Giant Gap Ravine, at an elevation of 800 to 900 feet above the river, or about 2600 to 2700 feet above sea level, contains masses of serpentine agglomerate similar to that in an unnamed ravine on this, the north side of the river. I talked to a few hardy hikers about an exploration, but to no avail, and even got into the lower reaches of the ravine, near the Gold Ring Mine, with my son and stepson, over the summer, but, no. So yesterday morning I sipped my coffee and mused somewhat as follows:

"It is almost eight in the morning; the first game of the World Series begins around five in the afternoon; I could have breakfast, throw some stuff in the pack, hit the trail by nine o'clock, blaze on down to the bridge site, ford the river, ascend the Green Valley Trail on the south side, cut over into Giant Gap Ravine about 1000 feet above the river and then follow down to the desired 800- to 900-foot level; find the agglomerate, if any, and then make my way back down to the river, ford it, and climb back up and out. There would be about 3000 feet of elevation gain and I would be thrashed, but, having waited for over twenty years, enough is enough. And then, in state of dream-like, anguished stupor, I could watch the game"

So that is what I did. By nine o'clock the chill was off the air, and, clad in jeans and a T-shirt, I set off down the trail, my Australian Shepherd, Lucky, leading the way, yipping and yelping in anxious glee. I took note of large fresh logs of bear poop all along the trail. Lucky had given his bear bark the night before, here was sign of the innocent culprit. It took about half an hour to make the river at the old suspension bridge site. This bridge was re-built by Joe Steiner around 1940 and was ripped out by the 1956 flood event, even though it was about 400 feet above normal river level.

The cables are still where the river left them, trailing downstream, high on the bouldery banks. Here the Green Valley Blue Gravel Gold Mining Co. (GVBGM) worked the principal hydraulic mine on the north side of the river, dumping huge quantities of large boulders into the river, and stacking up many other large boulders in piles. A series of cuts in the underlying serpentine bedrock mark where their sluice boxes were set.

I stuffed my shoes in my pack and picked my way through the frigid water over slippery boulders and took a brief break on the far side, where some masses of cemented glacial outwash form a terrace just above the river. I fired up my GPS unit, obtaining good satellite coverage, and began my climb. In a couple hundred yards the Green Valley Trail forks left, marked by a strange plastic stake with a Forest Service symbol, but no name. Strange as it seems to me, anyway, I had never hiked this part of this trail. It passes many areas where deposits of glacial outwash were mined by ground-sluicing, the poor cousin of hydraulic mining.

The typical ground-sluicing set-up is more or less as follows. One has a small but goodly amount of water above the sediments to be mined. A wooden sluice-box is set below the deposit of sediments, so anything washed away from the deposit has to go through the sluice box. A canvas hose with some kind of nozzle is used to conduct the water, under fairly low pressure, to the work. You just blast away at the sediments until they are all gone, and bedrock is exposed, removing whatever boulders which are too large for the sluice box as they are encountered, and stacking them nearby. Finally, clean up whatever gold has lodged in the sluice box, and then meticulously "clean" the exposed bedrock, digging out all crevices and pockets, and running this last, possibly most-precious fraction of the deposit through the sluice box, under very low flow so as not to inadvertently lose any gold. Clean up the box again and you are done.

I passed many such areas. Springs associated with the outwash deposits have nourished large thickets of Western Azalea which must make a stupendous display of flowers in April and May. As I climbed, I took careful note of my elevation, knowing that the (lowest) accordant terraces of outwash on both sides of the river here topped out at about 2000', or 200' above the river. I could occasionally see the terrace of the GVBGM across the river, and as I climbed above its level, was surprised to see that the little mines continued unabated, with rather substantial deposits of outwash. These deposits continued all the way up to the 2200' contour and slightly above. One passes a small reservoir with a stone dam and then the trail briefly coincides with a mining ditch which comes from Giant Gap Ravine, out of view to the west.

Dave Lawler and I had descended this southern part of the Green Valley Trail to exactly this point, seven years ago or so, and had followed this same ditch east into and then out of McIntyre Ravine, on our way to the Hayden Hill Mine.

I continued up the trail, wanting to gain more elevation before breaking away into Giant Gap Ravine. Suddenly every vestige of glacial outwash was gone. The trail began veering more and more east, towards McIntyre Ravine and away from Giant Gap Ravine. I decided to leave the trail and begin my exploration of terra incognita immediately, trying to gain elevation as I traversed the steep slopes.

At first this worked out OK, and I followed a bear trail with indications it might once have been a human trail, but soon enough, as more westerly exposures were reached, the forest of Douglas Fir thinned and more and more in the way of White-leaf Manzanita and scrubby Bay Laurel and other shrubs were met, along with occasional outcrops of serpentine, and I found myself forced downhill. I tried to at least hold a contour but it proved too difficult. Knowing the ditch was somewhere below, and assuming it could at least be followed easily enough into Giant Gap Ravine, I finally stopped the steep sidehill battle and let myself sag down to the ditch. Reaching the ditch, I found myself only a few yards from its source in Giant Gap Ravine, at perhaps 2280' or 2300' in elevation.

I should say that quite generally, on these more north-facing slopes on the south side of the river, the forest is lusher, and the soils deeper, than on the sun-scalded slopes north of the river. Here in the ravine itself, I found a surprisingly strong flow of water, and a jungle of Bigleaf Maple, White Alder, Creek Dogwood, and scattered large Canyon Live Oak, Incense Cedar, and Douglas Fir. I began following up the creek, staying mostly on the east side. It was difficult going due to the thickness of the vegetation, the large fallen trees, and mossy massive serpentine talus deposits.

The creek rose rapidly in elevation and in about a quarter mile, at about 2600' elevation, I saw my first serpentine agglomerate, in the bed of the creek. A few yards upstream a cliffy mass of agglomerate stood on the west side of the creek.

Continuing up, from the east side of the creek I saw dimly, through the thickets of dogwood, other masses of agglomerate, often covered in moss so I could not be sure of just what they were, with all the intervening foliage. I noticed a large number of very small Torreya californica, or California Nutmeg, all less than six feet tall, but no larger specimens at all. The gradient of the creek abated and a broad bouldery floodplain of alluvium made up the floor of the ravine, fifty yards across in places, riven by multiple channels, and absolutely choked with riparian vegetation. The conifers had increased in size, and I saw many Incense Cedar and Douglas Fir verging upon four feet in trunk diameter. At a certain point I abandoned the east bank and crossed this miniature floodplain to the west bank.

To my surprise, a large cliff of agglomerate stood there, which cost me a devil of a time to reach, threading through criss-crossing trunks of dogwood and fallen trees, like a drunken needle. Several distinct strata of agglomerate made up the cliff, really only about 60 feet high, the strata dipping gently to the north, towards the river far below. At the base of the cliff were once-twin Torreyas, each about two feet in diameter and perhaps 80' high, but one had broken down in heavy snow, and was stump-sprouting vigorously. I rested here for a time, and made explorations of the immediate area, circling to the top of the cliff, and to a spring doubtless associated with other, unseen masses of agglomerate, to the north, where other good-sized Torreyas grew near a White Alder fully three feet in diameter.

The Torreya is a conifer in the Yew family, with stiff sharply-pointed needles. Instead of a cone containing many seeds, there is a single drupe which much resembles a heft green olive. The bark is thin and light brown in color. These trees are somewhat rare, and are regarded as a threatened species. They are very slow-growing, and the little ones I saw, less than six feet tall, may have been thirty years old. This species of Torreya is confined entirely to California.

It was nearing one in the afternoon, and I decided against further exploration of Giant Gap Ravine, contenting myself with descending the west side, so as to verify that the cryptic mossy masses I had sometimes glimpsed were, indeed, agglomerate. They are.

The glacial outwash deposits of Green Valley clearly derive from several to many distinct episodes of glaciation. That they are outwash deposits, not moraines, is shown by their stratification—moraines are quite visibly unsorted and unstratified. Perhaps the North Fork glacier, which formed time and time again, reached as far down as Green Valley once or twice, but there is no direct evidence of that yet known.

The highest known outwash terrace is at the Hayden Hill Mine, and the top of the terrace is 600 feet above the present river. A relict channel in the serpentine bedrock beside this terrace fragment is about 400 feet above the present river. The way I see it, during whatever episode of glaciation from which the Hayden Hill terrace derives, there was a floodplain of outwash in Green Valley at that exact level. All the ravines leading into Green Valley carry a fair amount of rocky debris shed from the weak, steep serpentine slopes above. When an outwash plain develops, something like an alluvial fan would form within each ravine, backing up from the outwash plain. The parts of these alluvial fans in close proximity to the underlying serpentine bedrock became cemented by the same poorly-understood processes which also cemented similar portions of the glacial outwash deposits themselves. The agglomerate is characterized by a complete absence of outwash boulders, and is formed by about 95% or more mostly angular serpentine rocks and boulders, with perhaps 5% rounded boulders and cobbles of andesite which came from the heads of the ravines, where the "young volcanics" cap the ridge crests.

The serpentine agglomerate in Giant Gap Ravine is perfectly accordant in elevation with that in the ravine on the north side of the river, where the cave with the collapsed table and other artifacts of two periods of human occupation are found. My guess is that these two accordant masses of agglomerate, on opposite sides of the canyon, are both of the same age as the Hayden Hill outwash terrace. Taking a wild guess, this may have been as much as 800,000 years ago, during the famous and mysterious "Sherwin" glaciation.

Reaching the ditch, I followed it back out and around to the trail, and retraced my path to the bridge site, and forded the icy stream. Throughout all this time of the year, the sun does not hit the river much at all near the bridge, and cold air hangs around down there, and in the winter, frost which forms will sometimes last for weeks on end.


Climbing up the West Trail, as I reached the level of the lowest terrace top, 200' above the river, I decided to explore west, to the site of the funky plastic-tarp cabin, where various homeless ex-felons had found refuge from the early 1980s until quite recently. The side trail to the cabin site was overgrown, confirming my overall impression that nobody lives there anymore. I lopped away branches and soon enough reached the site. Since it is almost directly south of The Pyramid, and it is a lovely place, let's call it Pyramid Camp. Unfortunately it is strewn with garbage, old sleeping bags, bed frames, cans and bottles and plastic stuff. So it is one of about four sites in Green Valley, north of the river, which need cleaned up. It is directly above the steep banks of the GVBGM.

From Pyramid Camp a trail follows a shallow old mining ditch west along the top of the banks. I worked on this trail, and reached a really lovely vista point, with a view of Giant Gap and the Pinnacles. I took a few photos and then retraced my steps, lopping more branches, back to the main West Trail. Then it was up and very slowly out. I reached the top around 4:15 and changed into dry, clean, non-sweaty clothes, and collapsed on the couch, and watched the first game of the World Series, with happy results.


Such was a visit to Green Valley and Giant Gap Ravine.

Cheers,

Russell Towle


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