GLACIATION OF THE KAWEAH BASIN: KAWEAH GLACIER SYSTEM
In both the Wisconsin and El Portal Stages of the Pleistocene, the numerous converging canyons of the Kaweah Basin became pathways for cascading ice streams. However, inasmuch as even the larger of these streams attained lengths of only 10 miles, they fell short by many miles of uniting into a single Kaweah Basin glacier system or of forming a major trunk glacier comparable to the ones in the main drainage basins to the north and in the Kern Basin to the east. Because only the ice streams of adjacent tributary canyons united, there formed, instead, a series of separate glacier systems of relatively small extentone or more in the headward areas of each of the main branches of the Kaweah Basin: the Marble Fork, the Middle Fork, the East Fork, and the South Fork. These were branching glaciers that only locally, in their upper reaches, overswept the divides; elsewhere they were confined to the canyons, which were filled only in part.
The lower limits of the Wisconsin glaciers are clearly marked, for the most part, by distinct moraines, and these indicate that the termini of the principal ice streams reached altitudes as low as 5,200 to 8,200 feet. The exact extent of El Portal glaciers is unknown and may never be known, for terminal moraines are lacking, and the lateral moraines are partly concealed by dense chaparral on the lower slopes of the canyons. However, the approximate lower limits of glaciation can be inferred from the available evidence, and, for the principal ice streams, they lay at altitudes of 4,550 to 6,500 feetmarking limits which were considerably lower, therefore, than the corresponding ones of the Wisconsin glaciation.
The limited development of the Pleistocene glaciers of the Kaweah Basin is not surprising, since this basin heads not along the main Sierra crest, as do the adjacent Kings and Kern Basins, but rather along secondary ridges 12 or more miles farther to the westthat is, this basin extends only part way up the Sierra west slope. To be sure, at the east edge of the Kaweah Basin the glacial sources lay along the bold Great Western Divide, whose peaks have altitudes of 11,000 to over 12,500 feet, not greatly inferior to those of the main crest. But elsewhere the glacial sources of the Kaweah Basin lay along secondary ridges which branch off from the Great Western Divide and are, for the most part, much lower. One of these ridges, which includes a segment called Silliman crest, extends northwestward from Triple Divide Peak and forms a part of the north east rim of the Kaweah Basin. From this ridge, at altitudes of 10,000 to 11,600 feet, several ice streams descended into the northeasterly part of the Kaweah Basin. Another ridge, winding southwestward and southward from Florence Peak, forms the east rim of the South Fork Basin. Though for the most part only 9,000 to 11,500 feet in altitude, this ridge also gave rise to glaciers, and these descended into the canyons of the East Fork and the South Fork.
Only in the lower Kaweah Canyon were deposits found which appear to represent the earliest, or Glacier Point, stage of glaciation. Location of these deposits is not shown on plate 1 but is indicated on page A30. The deposits, being outwash materials laid down a considerable distance beyond the termini of the glaciers, give little beyond a suggestion concerning the nature and extent of this ancient glaciation in the Kaweah Basin.
The Marble Fork glacier was one of the principal ice masses in the Kaweah Basin, reaching a length of over 9 miles and extending down Kaweah Canyon to an altitude of about 5,350 feet. The trunk glacier, in the canyon, was fed by several short tributaries from the south, which originated at altitudes of 10,000 to more than 11,000 feet on the upland bearing Alta Peak (fig. 30), and by several considerably longer tributaries from the northeast, which originated on the ridge which bears the Tableland (11,000-11,600 ft) and Silliman Crest (10,000-11,200 ft). Because of the disparity in size between the southern and northern tributaries, the glacier system as a whole had an asymmetrical pattern. The northern tributaries were confluent, across a few low places on the divide, with the heads of the Kings River glacier system; and southeast of Table Meadows an icefield 2-1/2 miles wide connected the Marble Fork glacier with the Buck Canyon glacier, a member of the Middle Kaweah glacier system.
The valleys of Silliman Creek and Clover Creek also contained glaciers, but because these were shallow ice bodies only 2-1/2 and 3 miles long, respectively, they did not join the trunk glacier.
Wisconsin moraine plasters the slopes along the road connecting Giant Forest and Lodge Pole and across the valley from this road. In upper Silliman Creek valley, massive embankments of Wisconsin moraine lie on both sides of the creek, and a high steep-fronted moraine that flanks the lower edge of Cahoon Meadow is trenched by the creek. In Clover Creek valley also, the main loop of Wisconsin moraine is complete, extending back as far as the mouth of the unglaciated West Fork.
The effects of vigorous glacial erosion in predominantly massive exfoliating granite are strikingly shown both in the clean-swept area extending from Tokopah Valley to the Tableland and in the vicinity of picturesque Heather, Pear, and Emerald Lakes, which lie in compound cirques. These lakes are typical tarns and are held in by barriers of massive granite. In places on the cirque walls back of these lakes the upper limit of glaciation is very plain; sheer cliffs of frost-shattered granite come down to the smoothly sloping platform that was abraded by the moving ice. The bowl of the cirque is very imperfect because of the many ledges of massive granite that could not be eroded away. The rocks have been rounded and smoothed to pillowlike forms. Aster Lake, the small tarn below Emerald Lake, provides a good example of selective quarrying, being itself encased between masses of solid, very sparsely jointed granite.
The little valley southwest of Heather Lake held a small glacier that did not quite join the master glacier in Tokopah Valley. This valley heads in a poorly shaped cirque which may be described as a veritable glacial quarry. There the glacier left enormous quantities of quarried blocks in a terrific jumble, gleaming white among the forest trees.
The Marble Fork glacier in El Portal Stage was over 10 miles long and 25 miles square, and it reached down Kaweah Canyon to an altitude of 5,350 feet. It was joined, far downstream, by its major affluents, the Silliman Creek and Clover Creek glaciers. That these glaciers were confluent with the trunk glacier in El Portal Stage is indicated by remnants of older drift scattered over the lower slopes of both valleys.
The road from Giant Forest to Lodge Pole crosses the fairly heavy and bouldery left lateral El Portal moraine near the Wolverton Creek bridge; on the north side of the valley, in the vicinity of Willow Meadow, the J. O. Pass Trail crosses the right lateral moraine. Inasmuch as Willow Meadow lies among older moraines, some of them fairly prominent, it is evident that this divide was overswept by the earlier ice.
Seven miles below the terminus of the Marble Canyon glacierthat is, about half a mile above Ash Mountain headquartersa deposit of material interpreted as bouldery outwash of El Portal Stage is revealed in a roadcut on the Generals Highway (Matthes, 1950a, p. 52).2 (See fig. 31.) This material is believed to have been washed down from El Portal glaciers in the upper canyons, probably not only those in the Marble Fork but also those in the Middle Fork. The material was deposited in the streambed but, as a result of continued trenching by the river, it is now about 100 feet up the canyon side. Evidently this deposit is of considerable age, for all the boulders have rusty surfaces, some of them are partly decomposed, and the interstitial sand is stained reddish brown by iron oxide.
In the lower Kaweah Canyon, considerable masses of material, presumably outwash of the Glacier Point Stage, remain. (See fig. 32.) These masses occur as inconspicuous terraces on the side of the canyon about 200 feet above the river bed, and they are exposed in several roadcuts along the Generals Highway.
The great antiquity of these deposits is evident from the fact that all the boulders except the surface ones are completely decomposed and can be cut through like so much granite sand. In making these roadcuts, no blasting or crowbar work was necessary; a Civilian Conservation Corp crew with picks and spades cut with ease through the decayed boulders and the interstitial sand and shaved them back to a uniform, smooth slope. Rainwater rills have since carved little furrows in that slope, trenching both the boulders and the matrix around them to equal depth. Paradoxical as it may seem, the tops of the uppermost boulders, which project slightly above the surface of the deposit, still remain firm and would require a blow with a sledge hammer to be broken. They survive in the form of convex caps because they are in well-drained positions and are frequently exposed to the drying rays of the sun.
During both the earlier and the later glacial stages, the converging valleys at the head of the Middle Fork Canyon were occupied by ice streams that attained sufficient length to unite into a short trunk glacier in the main canyon, below Redwood Meadow. (See fig. 33.) The glaciers of both stages were confined to their respective canyons, nowhere overflowing onto the higher parts of the intervening divides. The largest ice streams, those of the Middle Fork proper and of Cliff Creek, attained lengths of approximately 10 miles in the earlier stage and 9 miles in the later stage. The principal sources of ice lay to the east, in cirques on the Great Western Divide; however, several other sources lay on the secondary divides to the north and south. In the earlier stage, the lowest altitude reached by the trunk glacier, in Middle Fork Canyon, was about 4,800 feet; in the later stage, about 5,200 feet.
Moraines deposited by the earlier Middle Fork glacier system are found in the vicinity of Redwood Meadow, which is in the triangular area between Middle Fork Creek and Cliff Fork Creek. The grove of Big Trees which gives the name to this meadow stands mainly on older drift, and old moraines also enclose the grove on both sides. A second grove, about a mile farther up Cliff Creek on the north side of the stream, stands partly on older moraine and partly above its limits.
Wisconsin moraines are also conspicuous in the vicinity of Redwood Meadow. The trail from Redwood Meadow to Little Bearpaw Meadow crosses the left lateral moraine of Middle Fork glacier. Farther to the southeast is the right lateral moraine of the Cliff Creek glacier. Big Trees stand on both of these ridges.
In Middle Fork valley, which is littered with Wisconsin morainal debris, the trail from Little Bearpaw Meadow descends through the depression back of the right lateral moraine, a ridge about 100 feet high. The trail crosses the moraine by way of a gap cut by the stream flowing from the meadow. Southwest of the gap, the moraine is less prominent. On the opposite side of the valley, the Wisconsin moraines have a distinct upper limit, above which are smooth mountain slopes densely covered with brush. In this section of the valley, glacial outwash forms terraces about 50 feet high on both sides of the Middle Fork.
The Hamilton Lakes locality, in the upper reaches of the Middle Fork Basin, impressively illustrates the erosional effects of glaciation and concomitant snow avalanching (fig. 34, frontispiece). The large lower lake (altitude 8,300 ft)occupying a rock bowl with a smooth glaciated lip, clearly visible under the watermarks the place of confluence of glacial tributaries that issued from three cirques lying 1,700 to 2,000 feet higher. These tributaries excavated the lake basin in what is really a canyon step. Northwest of the lake, massive granite, cleft by nearly vertical joints, has been sculptured into pinnacles somewhat El Capitan-like in aspect, but more complex (fig. 35). In the vicinity of this lake, the effects of snow avalanches are evident on every hand. One avalanche chute northeast of the lake outlet has not only an avalanche cone beneath it but also a dump in the lake, visible from the trail above.
In the valley of Cliff Creek, terraces of glacial outwash 50 to 60 feet high occur near the junction with Timber Gap Creek. The trail enters the valley of Timber Gap Creek by climbing steeply over a gigantic moraine. Through this ridge the creek has cut a narrow gulch with steep bouldery sides.
In addition to the main glacier system, independent ice bodies of small size developed in the Middle Fork Basin during both glacial stages. On the north side of the basin, glaciers formed in upper Mehrten Creek Valley, Buck Canyon, and the two intervening valleys. On the south side of the basin, a single small glacier formed in the valley of Little Sand Meadow.
At the head of Mehrten Creek, southwest of Alta Peak, Wisconsin glaciation is recorded by an imperfect cirque containing a small quantity of jumbled morainal material. On the slopes below this cirque, along the Sevenmile Hill trail, are scattered morainal materials of the earlier glaciation.
In the adjacent valley, which contains Alta Meadow, the glacial record is much clearer. Here, at the lower margin of another shallow cirque, lie at least three Wisconsin moraines. They are composed of angular rock blocks, and each morainal loop protects a sloping shelf on its upslope side. Below these moraines, deposits of the earlier stage extend far down the mountainside. The High Sierra Trail crosses the older moraines, which are cut by a steep-sided gulch.
Alta Peak, the summit which bore these glaciers, has a highly asymmetric profile, its northern slopes having been vigorously glaciated and its southern slopes only mildly so (fig. 30).
A considerably larger glacier occupied Buck Canyon during both glaciations. As previously noted, the broad icefield at the head of this glacier was confluent with the Marble Fork glacier system. In the earlier stage, the ice descended the canyon a distance of 5 miles, to an altitude of 5,600 feet. The tapering ice tongue of this glacier was joined by a tributary, more than 3 miles long, that originated in a cirque northeast of Alta Peak. In the later stage, the Buck Canyon glacier was somewhat shorter, and its terminus reached only to 6,000 feet. The tributary from northwest of Alta Peak was then only 1-1/2 miles long and therefore remained a separate glacier. The High Sierra Trail, from Giant Forest to Bearpaw Meadow, crosses Buck Creek and ascends the Wisconsin left lateral moraine deposited by the Buck Canyon glaciera fairly sharp moraineand then traverses older moraines plastered against the valley side. The latter moraines, however, do not reach to the top of the ridge between Buck Canyon and the valley of the Middle Fork.
Glaciation occurred during both the Wisconsin and the El Portal Stages of the Pleistocene in the upper basin of the East Fork, not only in the main valley itself (in the Mineral King region, outside of Sequoia National Park) but also in the large tributary valley of Horse Creek.
The main valley held a many-branched glacier which, in the earlier stage, was almost 10 miles long and descended to 4,950 feet and, in the later stage, was 6 miles long and descended to 6,850 feet. The trunk glacier was fed by long, narrow tributaries, some originating at the east, in cirques on the Great Western Divide, but most originating at the south, on the secondary ridge extending westward from Florence Peak on the Great Western Divide. In the asymmetary of its pattern, the glacier system of the East Fork somewhat resembled that of the Marble Fork, with the obvious difference that the principal sources of the East Fork were on the south side of the basin instead of on the north. Indeed, the amount of ice contributed to the East Fork glacier system from the north was negligible.
During the Wisconsin Stage the most westerly tributaries of the East Fork glacier system remained as small independent glaciers. Two of these were in the upper valleys of Deer Creek.
Older moraines of the East Fork glacier occur along the road which ascends the north side of the valley. They begin at a point about 1 mile east of Silver City and continue eastward for a distance of more than 2 miles. The road enters Wisconsin deposits near the junction of the Mosquito Lakes outlet with the East Fork, and bouldery moraines of this age continue upstream to the bend of the river near Mineral King. In places these moraines have been trenched by the river. The absence of conspicuous moraines in some of the upper tributary valleys, as in the vicinity of Farewell Gap, may be attributed to two circumstances: the small size of the rock fragments derived from the metamorphic rocks which prevail here, and the changes wrought by periodic snowslides. The trail to Eagle Lake climbs a fairly smooth slope of moraine consisting mostly of small fragments and slabs of metamorphic rocks and only a scattering of granitic boulders. This entire valley appears to be sheathed with such materials.
The earlier Horse Creek glacier was about 6-1/2 miles long and descended to 5,700 feet; the later one was about 5 miles long and descended to 6,650 feet. Most of the ice came from broad, shallow cirques to the northeast and east, but in the earlier stage, ice from the valley of Whitman Creek spilled over the north edge of the Hockett Meadows northwest of the Hockett Ranger Station, cascaded down the slope several thousand feet, and, 5 miles from its source, joined the Horse Creek glacier. In the Wisconsin Stage the Whitman Creek glacier fell just short of uniting with the Horse Creek glacier, as indicated by the moraines which extend to the lip of the Whitman Creek valley and describe their farthermost loop where this valley begins to drop off from the level of the plateau.
Northeast of Evelyn Lake is a little cirque in the lee of a summit only 8,900 feet in altitude (the actual rock rim of the cirque is at 8,700 ft.). In the earlier stage, this cirque contributed ice to the Horse Creek glacier; in the later stage, the cirque held a small independent ice body. The lower trail to Cahoon Meadow crosses the Wisconsin moraines of this glacier. Evelyn Lake occupies a steep-walled cirque which held, during both stages, a glacier formed in the lee of a plateau summit 9,100 feet in altitude. Large Wisconsin moraines composed of big angular blocks border the lake and extend about half a mile down the canyon; below these moraines lie older ones which are crossed by the trail to Cahoon Meadows. The features at Evelyn Lake well illustrate the effectiveness of erosion by even a small glacier. Furthermore, this glacier and its small neighbor are of special interest because of the low altitudes at which they originated.
The upper South Fork Basin was occupied, during both glacial stages, by an irregularly shaped compound ice mass. In the earlier stage this glacier not only discharged down the canyon of the South Fork but also was continuous with the Whitman Creek glacier northward through Hockett Meadows. The South Fork was then 8-1/2 miles long, measured from its source above the Blossom Lakes to its terminus at 6,200 feet in the South Fork Canyon. In the later stage this glacier was a mile shorter and extended down only to 7,500 feet.
This broad, shallow ice mass left a covering of moraines and scattered debris on the country across which it spread. Some of these deposits are crossed by the trail from Wet Meadow to Hockett Ranger Station. Ice advancing from the vicinity of Sand Meadow scooped out the shallow basins of the Hockett Lakes, overrode the ridge to the west of these lakes, and spilled down into South Fork Canyon.
From the evidence of glacial boulders which strew Tuohy Meadow and the South Fork Meadows, it is clear that all of this part of the South Fork basin was covered by ice streams converging from the numerous pockets in the high southern and southeastern rims of the plateau.
During both stages, a small isolated glacier lay on the north side of the peak (9,405 ft.) at the northeast end of Dennison Ridge. The trail leading from the Hockett Lakes to the Garfield Grove of Big Trees crosses the moraines of this glacier.
The so-called "sand dune" which gives name to Sand Meadows is a nearly circular, rounded deposit composed of sand, subangular gravel, cobbles, and boulders as much as 9 inches in diameter (fig. 36). The dune is obviously not aeolian but is the remnant of an outwash deposit formed late in the Wisconsin Stage when the meadow lay under a shallow wasting ice sheet. A stream of meltwater probably deposited the material in an embayment of the ice mass. When the ice melted, the deposit was left without supporting walls, and under the influence of gravity and rainwash it gradually assumed its present oval form. To the southeast of this deposit are two much smaller and flatter deposits of similar material. Both are still largely bare of vegetation but are being encroached upon. The main "dune" bears no vegetation whatever but is surrounded by a carpet of xerophytes and a partial circle of small lodgepole pine. East of the main dune, in a fringe of timber on a low rock ridge covered with Wisconsin moraines, is a small spur that is composed also of gravel and cobbles mixed with sand. This spur may be a record of the glacial stream channel through which the sand, gravel, and coarser materials were washed out to the main "dune."
Last Updated: 03-Aug-2009