During the Pleistocene epoch, the higher parts of the San Joaquin Basin, like those of the other basins on the west slope of the Sierra Nevada, were mantled repeatedly with glaciers.12 Practically all of the glacial sculpturing that gives the High Sierra its distinctive scenic aspect, has been superimposed on a landscape inherited from Miocene and Pliocene times (Matthes, 1933a, p. 37). While the San Joaquin River was cutting its sharply V-shaped gorge in the lower slope of the Sierra, the untrenched Pliocene valleys of the upper slope were being vigorously glaciated and transformed into broadly U-shaped troughs. The little side valleys on the Miocene uplands, which already were hanging above the Pliocene main valleys, were occupied by tributary glaciers and as the side valleys underwent less excavation than the main valleys, the discordance between the two was generally increased. The heads of the little Miocene valleys carved in the flanks of the High Sierra crests were resculptured into amphitheaterlike cirques. The latter were cut deeply into the tabular remnants of the Eocene surface that persisted on the higher peaks, but on Mount Darwin and Mount Wallace, the remnants were not wholly consumed. These summits escaped glaciation and were subject only to nivation.
Distribution of the late Pleistocene (Wisconsin) glaciers for the entire Sierra Nevada is shown on an inset map printed on Sheet No. V of the Geologic Map of California (scale 1:500,000), published by the Division of Mines, California Department of Natural Resources, San Francisco, 1938. The north half of this glacial map is by Eliot Blackwelder 1932), the south half by F. E. Matthes (1937).
In the San Joaquin Basin the same method was employed for tracing and mapping the courses of the ancient glaciers and for determining the farthest limits which they had reached that had proved effective, previously, in the Merced and Tuolumne basins. That method relies on the testimony of glacial deposits rather than on that of sculptured features, and consists primarily of a systematic survey of the moraines which were built by the individual glaciers.
In open country, such a survey can be executed readily with sufficient accuracy for a reconnaissance map on the scale of 1:125,000 by locating the moraines by eye with respect to identifiable landmarks; but in the forested tracts, the more important moraines must be actually followed out, and, in some places, even located by traversea laborious and time-consuming process. Fortunately, the forested areas in the San Joaquin Basin, though of considerable extent, are so amply diversified by topographic drainage features, as well as by occasional meadows, that no traversing was needed, and a large share of the work could be done by following the moraines, or the swales between moraines, on horseback. In the rougher areas, of course, the mapping had to be done on foot.
In spite of the rapidity with which the survey was carried out in a rugged mountain region largely devoid of roads, and only scantily traversed by trails, the resulting map (pl. 1) is probably of more than reconnaissance accuracy, for it shows not merely the areas that were formerly ice covered but also, by rows of dots, the crestlines of the individual moraines of the later glaciation. These crestlines, it is evident, tell the story of the glacial invasions, and the minor fluctuations of the glaciers, more precisely and more graphically than can mere words.
In the central part of the basin, which contains the outer fringes of the glaciated territory, special pains were taken in the mapping of the glacial deposits, as a definite knowledge of the extreme limits of glaciation is of paramount importance in the correct analysis of the landscape. It was necessary to do this work with more care as the outermost glacial deposits in most places are older than the Wisconsin and generally consist of small, obscure patches no longer identifiable by their topographic forms. It is due largely to that circumstance that the true extent of the former glacial mantle of the Sierra Nevada long remained in doubt and a subject of misconceptions.
Reliance was not placed on topographic forms as possible indicators of changes wrought by glacial erosion because, as had been learned in the Yosemite region and in the Tuolumne Basin (Matthes, 1930a, p. 89-91), the extraordinarily varied joint systems in the granitic rocks of the Sierra Nevada in large measure controlled the eroding action of the ice. The joints more than any other factor determined whether a V-shaped river canyon would or would not be transformed into a typical U-shaped trough. Where the granite is thoroughly divided by joints (figs. 28, 29), glacial plucking, or quarrying, was particularly effective and typical glacial forms were actually produced; but where the joint features are spaced far apart, or are wholly absent over distances of hundreds and even thousands of feet, glacial action was reduced largely to abrasion, and only minor changes were effected in the valley form. Even the Tuolumne Glacier, which attained a length of 60 miles and a depth of 4,000 feet, failed to give its canyon a typical U-shaped form throughout, because the walls, for mile after mile, are composed of prevailingly massive granite.
It was discovered also, in the Yosemite region, that hanging valleys, on the western slope of the Sierra Nevada, are not necessarily indicative of profound glacial erosion, many of them having gained their hanging aspect long before the glaciers appeared upon the scene, simply as a result of rejuvenation of the master stream induced by the tilting of the Sierra block. Many hanging side valleys occur in the lower, unglaciated courses of the main canyons as well as in the intensely glaciated upper courses.
In the San Joaquin Basin, therefore, it likewise was deemed best to regard the varying forms of the canyons and, indeed, of all the features of the glaciated landscape, as things to be explained rather than as features diagnostic of past events.
In the morainal deposits of the San Joaquin Basin, as in the Yosemite region, abundant and unmistakable evidence was found of two distinct stages of glaciation separated by a lengthy time interval; also meager indications of a third, very early stage (Matthes, 1929). Many examinations of the morainal deposits of the two easily recognizable glacial stages in this basin confirm the interpretations of the moraine systems of the Yosemite and Tuolumne regions and help establish the succession of events making up the glacial history of the west slope of the Sierra.
It should be added that in later years much corroborative evidence has been found in the Kings River, Kaweah, and Kern Basins. Throughout, the south-central Sierra Nevada, therefore, the morainic systems of the great trunk glaciers and their numerous branches spell out the same story of three distinct, stages of extensive and long-continued glaciation during the Pleistocene epoch.
For discriminating between moraines belonging to the different stages of glaciation it was found best, in the San Joaquin Basin, to apply the criteria which the writer had developed in the course of his detailed studies of the Yosemite region, because the general nature of the country in the two areas, the character of their rocks, the climatic conditions, the vegetal cover, and the soils are closely similar.
On the glacial map (pl. 1) distinction is made only between the Wisconsin and pre-Wisconsin stages. Although at some localities (see pages 56, 57-58) the field data appear to warrant subdivision of the Wisconsin moraines into those of early Wisconsin time and those of late Wisconsin time, corresponding to the Tahoe and Tioga stages of Blackwelder (1932), such division could not, in the time available for the reconnaissance surveys, be carried consistently over the entire area. In many places the moraines of early and late Wisconsin time are so closely alike that their separate mapping would have required detailed and prolonged study. All the moraines of the Wisconsin stage are therefore shown on the map provisionally as a single unit. The data, nevertheless, are sufficiently detailed to permit individual moraine crests to be indicated by rows of dots.13
The moraines of the Wisconsin stage as a rule are well preserved, sharp-crested, and studded with fresh looking unweathered boulders. A few weathered and even thoroughly decomposed boulders occur, but it is evident from their sparse occurrence in deposits composed almost wholly of fresh, unweathered rocks that ring under the hammer, that the weathered boulders represent an admixture of material that already was considerably weathered when the glacier picked it up, perhaps from moraines of earlier glacial stages. It is significant, moreoever, that in these younger moraines not only the boulders of siliceous granite but even those of much weaker diorite and gabbro are essentially unweathered and unstained.
The pre-Wisconsin moraines in the San Joaquin Basin are in all respects closely similar to those in the Yosemite region, and are therefore referred to the El Portal stage. Compared to the moraines of the later stage, they are poorly preserved, and generally are cloaked with granite sand derived from their own disintegrating boulders. In places, the bouldery character of the ancient moraines is shown mainly in exposures made by uprooted trees. The boulders in the interior of the moraines are, as a rule, encased in ferruginous rinds; many are entirely decomposed, so that they may be cut with a shovel. Although originally of much greater bulk than the moraines of the Wisconsin stage, the older moraines have long since lost their crests, and their form has become subdued and flattened. Over considerable distances they have not only lost their ridgelike aspect but have become inconspicuous in the landscape. The accumulation of sand on the upslope sides of morainal ridges in some places has largely concealed them.
Terminal moraines of the El Portal stage appear to be generally absent in the main canyons on the west slope of the Sierra Nevada. At least, methodical search has failed to reveal any remnants of such moraines in the principal canyons of the Stanislaus, Tuolumne, Merced, San Joaquin, Kings, Kaweah, and Kern basins. Their total absence can hardly be explained as the result of post-El Portal stream erosion and collateral slope-wash, slumping, and other degrading processes; for in some of the canyons, notably in the San Joaquin Canyon, the local conditions are distinctly favorable for the preservation of at least the wings of terminal moraines and recessional moraines, but no vestiges of such remain. It seems probable, therefore, that the glaciers of the El Portal stage did not maintain their maximum extension long enough to build bulky terminal moraines.
The El Portal stage is believed to correspond to Blackwelders Sherwin stage at the east base of the range (Blackwelder, 1932), and is thought to be not younger than the Illinoian stage of the continental glaciation (Matthes, 1933b, p. 72, 76; 1935). In the San Joaquin Basin as in the Yosemite region, however, these older moraines differ considerably among themselves in degree of preservation and in the decomposition of their granitic boulders, and it therefore seems entirely possible that they include remnants of two or more as yet unseparated stages that differ considerably in age, including perhaps both the Kansan and the Illinoian (Matthes, 1933a, p. 33). Only intensive studies in selected areas are likely to settle that question. The correlation of the older glacial deposits of the Sierra Nevada must necessarily remain tentative until the glacial field of the Pacific ranges has been more closely connected with the glacial fields of the Rocky Mountains and the Great Plains.
No morainal deposits belonging to the Glacier Point stage, the earliest stage of glaciation that was recognized in the Yosemite region, are shown on the map; but it is not to be inferred from this that no deposits whatever of that early glaciation remain preserved in the San Joaquin Basin. A few small, isolated patches of an ancient moraine were discovered in the central portion of the basin, on a mountain summit at a high level above the surrounding canyons, and these may well be representative of the Glacier Point stage, in view of their elevated positions.14 The deposits of the Glacier Point stage thus far discovered, notably those in the type locality in the Yosemite region, on the divide to the east of Mount Starr King (Matthes, 1930a, p. 73-74), are situated at a great height above the neighboring canyons, which would seem to imply either that the Sierra Nevada at one time was fairly overwhelmed with ice, or that a great deal of canyon cutting has taken place since these ancient moraines were laid down. As the latter hypothesis seems the more probable of the two and finds support in a variety of circumstantial evidence, there is good reason for assigning the Glacier Point stage, together with Blackwelder's McGee stage, to the early Pleistocenepresumably corresponding to the Nebraskan stage (Matthes, 1933a, P. 33). In the San Joaquin Basin, meanwhile, until more conclusive proof is forthcoming that the isolated patches of morainal material mentioned are of decidedly greater antiquity than the deposits of El Portal age, it seems best not to differentiate them from the latter on the map.
The San Joaquin glacier system of the pre-Wisconsin stages was by far the largest system of confluent glaciers in the Sierra Nevada, measuring more than 50 miles in length along the crest of the range and 30 to 35 miles wide. Of the 1,760 square miles comprised in the San Joaquin Basin, almost 1,100 square miles were covered by glaciers. This ice mass, together with the ice masses in the basins of Dinkey Creek and the North Fork of the Kings River, formed a mer de glace 1,500 square miles in extent. Yet it was not an icecap, strictly speaking, for its surface was broadly concave rather than dome shaped. It consisted of a large number of confluent glaciers that had descended from the surrounding peaks and crests, filled the canyons, and overflowed onto the intermediate uplands (Matthes, 1947, p. 208; 1950b, p. 62).
The San Joaquin glacier system was essentially bilobate, in that it comprised two great primary branches that descended Middle Fork and South Fork canyons. The branches united below the junction of the two forks, to form a very broad trunk glacier that overflowed the main San Joaquin Canyon and spread widely over the central part of the basin northeast of Chiquito and Kaiser Ridges. The glacier ended in a rather blunt tongue, only a few miles long, which lay in that part of the main canyon which separates Chiquito and Kaiser Ridges. The length of the San Joaquin glacier system, measured from Muir Pass at the head of the South Fork branch to the terminus of the trunk glacier, 1-1/4 miles below the mouth of Rock Creek, was nearly 60 miles. The length measured along the Middle Fork branch was almost 45 miles. The shortness of the trunk glacier, which descended to a point about 14 miles below the junction of the Middle and South Forks, is explained by the fact that the ice which spread over the vast expanse of rolling uplands bordering the canyon was dissipated by ablation much more rapidly than it would have been if it had been concentrated in a deep cliff-shaded trench.
Ice was contributed not only from areas along the crest of the range but also from all sides of the various ridges on the west slope, except in the case of Chiquito Ridge, which, because of its low altitude (maximum 8,358 feet), developed glaciers only on its north side. The glaciers of the south side of Kaiser Ridge were tributary not to the main San Joaquin glacier system but to a separate and much smaller system in the basin of Big Creek.
MIDDLE FORK GLACIER
Middle Fork glacier, in conforming to the course of the canyon which it occupied, flowed successively northeast, southeast, south, and finally southwest, to its junction with the South Fork glacier. Its length, from its source on Mount Davis to its junction with the South Fork glacier, 1 mile southwest of Ballon Dome, which was overridden by the ice, was 31 miles.
In its upper course, the sources of this glacier lay at altitudes of 10,000 to over 13,000 feet on the north east slope of the Ritter Range, mainly in the basins of Thousand Island Lake, Garnet Lake, Shadow Creek, Minaret Creek, and King Creek. As these sources were situated to the west, of the main trunk, the upper part of Middle Fork glacier was highly assymetrical.
Farther downstream, Middle Fork glacier was augmented by large tributary glaciers, notably those in the valleys of Fish Creek, North Fork, and Granite Creek. These glaciers flied their valleys and, over-flowing the intervening divides, became confluent in most places.
Fish Creek glacier, which was 17-1/2 miles long, measured from Red and White Mountain to its junction with the Middle Fork glacier, originated, for the most part, in cirques ant altitudes of 10,000 to 12,000 feet on the main crest of the Sierra and on the north side of the Silver Divide. North Fork glacier, which was 16-1/2 miles long, measured from Rodgers Peak to its junction with the Middle Fork glacier was fed principally from areas on the southwest and south sides of the Ritter Range, and from basins at altitudes of 10,000 to 12,000 feet, on the southeast side of the nameless crest trending southwest from Mount Lyell. Granite Creek glacier, which as 14 miles long, measured along its west branch, had its main sources at altitudes of 9,500 to 11,000 feet on the crests which bear Black, Sing, Gale, and Triple Divide Peaks.
SOUTH FORK GLACIER
South Fork glacier, measured from the head of Evolution Creek at Muir Pass to its junction with Middle Fork glacier 1 mile southwest of Balloon Dome, was 16 miles long. Throughout most of its course it flowed northwestward, its consistent trend being in marked contrast to the course of the Middle Fork glacier. South Fork glacier received much of its ice from cirques on adjacent mountains and from its many tributary glaciers, most of which joined it from the east and northeast. The most important tributaries were Goddard Canyon glacier, Piute Creek glacier, Bear Creek glacier, and Mono Creek glacier.
The upper part of the South Fork glacier, which occupied Evolution Valley and Evolution Basin and therefore may be called the Evolution glacier, was 11 miles long, measured from Muir Pass to its junction with Goddard Canyon glacier. It was fed from cirques at altitudes of 11,500 to over 13,500 feet, located at its head along the main crest of the range, and from others on the high confining ridges, such as Glacier Divide and the nameless ridge which bears Mount McGee.
Goddard Canyon glacier was 8-1/2 miles long, measured from the divide south of Martha Lake to its junction with the Evolution glacier. Its sources lay in cirques at altitudes of 11,500 to 12,500 feet on the bordering ridges, especially on the LeConte Divide; but much ice was also contributed from the cirques at its head whose walls rose to the lofty summits of Mount Goddard and Mount Reinstein.
Piute Creek glacier, a branching ice body 11 miles long measured to its head on Mount Emerson, was fed mainly from several enormous compound cirques that ranged along the crest of the range at altitudes of 11,000 to over 13,000 feet, the largest of these, Humphrey's Basin, being more than 3 miles across. However, throughout the course of this glacier the lateral cirques along both sides contributed notably to its volumefor example those at 11,500 to 13,000 feet on the north slopes of Glacier Divide.
Bear Creek glacier and Mono Creek glacier were tributaries of even greater length and complexity. Bear Creek glacier was 15 miles long, measured up Hilgard Branch, and headed at altitudes of 10,000 to over 13,500 feet mainly in cirques on the south side of Mono Divide, and on the northwest side of a long curving nameless crest which bears Mount Senger and Mount Hooper. Mono Creek glacier was 20 miles long, measured to Mount Mills, and accordingly was the longest tributary of the South Fork glacier, and longer than any tributary of the Middle Fork glacier. Its most important sources lay on the main crest of the range, between Mount Abbott and Red and White Mountain, at altitudes of 10,000 to over 13,500 feet; others were located to the north on the Silver Divide, and to the south on the Mono Divide.
The union of the Middle Fork and South Fork glaciers produced an enormous volume of ice which overflowed the canyons and spread broadly across the plateaulike uplands, forming a practically continuous icefield.
At the northwest this icefield was augmented by several confluent glaciers which descended the valleys of Jackass Creek, Chiquito Creek, and other smaller southeastward flowing streams. The sources of these glaciers lay at altitudes of 8,000 to 10,000 feet on the northeast slope of Chiquito Ridge and on the southeast slope of the crest just north of Beasore and Mugler Meadows. The Chiquito Creek glacier, the largest of the group, was about 16 miles long, measured from Redtop Mountain to the San Joaquin Canyon at San Joaquin Bridge.
West of the junction of the Middle and South Fork glaciers, the ice was sufficiently deep to overtop the knobs and hills which rise 200 to over 800 feet above the uplandsJackass Butte, Jackass Rock, Squaw Dome, Cattle Mountain, and othersas shown by the scattering of erratics all the way to the summits of these eminences.
On the rolling country south of Jackass Meadows, erratics are in evidence almost everywhere, but there are no heavy concentrations of drift. Between the Placer Ranger Station and the San Joaquin Bridge, the gentle, smoothly rounded slopes of the lower Chiquito Creek basin are not visibly affected by the presence or absence of the drift (figs. 34, 35). Most of the interfluves are deeply cloaked with loose sand derived from disintegrating rockmuch of it, apparently from boulders in the older drift. Only here and there are patches of the drift exposed. Most of it consists of rounded, evidently water-worn pebbles and small cobbles, which are mixed with more irregularly shaped and typically glacial cobbles and boulders. Quartzite, schist, dark-colored porphyry, and lava are common, and in places are more abundant than granitic rocks.
Northeast of Mugler Meadow, where a wagon road crosses Chiquito Creek, glacially striated cobbles are present in profusion. There is, northeast of the crossing, what appears to be a terracelike deposit of gravel and boulders. In this area the schists are particularly well striated, but the granite cobbles are either unstriated or so slightly striated as not to serve as diagnostic glacial material. Quartzite and schist are plentiful, and are probably derived from the south slope of Black Peak, but no trace was found of lava such as occurs in the Jackass country, a few miles to the east. This drift may be younger than that of the earlier glaciation in the Jackass regionperhaps intermediate in age between that drift and the Wisconsin drift to the north. In any event it is not Wisconsin, since in most places it underlies smooth slopes covered with granite sand.
Important contributions to the central icefield were also made by glaciers that originated at altitudes of 9,000 to 10,500 feet on the north slope of Kaiser Ridge, and that filled the valleys of Kaiser Creek and neighboring streams on the upland. Older drift forms a more or less continuous veneer covering the slopes on both sides of Kaiser Creek, and it is present in large quantities in the neighborhood of Kaiser Creek Diggings, where it forms terraces or terracelike benches with very steep slopes facing the creek bed. Farther north, in the vicinity of Cow Meadow, the scattered erratics which are evidence of the earlier ice, are very sparse. Mount Tom was a nunatak, its summit rising 1,000 feet above the level of the surrounding ice.
LOWER SAN JOAQUIN GLACIER
Although the central icefield was restrained on the southwest and south by Chiquito Ridge and Kaiser Ridge, nevertheless it was not wholly confined by these barriers, but discharged southward through the gap between the two ridges, by way of the lower San Joaquin Canyon. The extent of this lobe must be inferred from remnants of its lateral moraines, since here, as in the other principal canyons of the west slope of the Sierra Nevada, there are no traces of El Portal terminal or recessional moraines. It appears that a blunt lobe about 2 miles wide pushed a little more than 3 miles, down the canyon to an altitude of about 2,600 feet, the lowest point reached by the ice in the San Joaquin Basin. Measured from the junction of the Middle and South Fork glaciers to its terminus, the San Joaquin trunk glacier was about 14 miles long.
GLACIERS IN BIG CREEK BASIN15
The Big Creek glacier system was distinct from the great San Joaquin glacier system. It attained a length of about 20 miles and an areal extent of about 105 square miles. The ice was derived in part from cirques at 9,000 to 10,500 feet on the south side of Kaiser Ridge, but principally from the broad shallow cirques situated at about the same altitudes on the uplands at the head of Big Creek basin. The ice streams converging from these sources coalesced into a small trunk glacier which pushed several miles down Big Creek Canyon, to an altitude of 3,100 feeta point almost as low as that reached by the neighboring San Joaquin trunk glacier. Thus the terminals of the two glacier systems approached each other but never united.
North and south of Huntington Lake, older drift is plastered against the slopes to heights of several hundred feet, except on those steeper places from which it has been removed. On the ridge northwest and north of Boneyard Meadow, older drift is present to within a few feet of the summit, that is, to altitudes over 7,700 feet. Crags on the summit (like those shown in figures 36 and 37) clearly show that in places rock has been stripped to a depth of 10 feet since the passage of the earlier ice; hence the absence of drift on some intermediate summits does not necessarily indicate that the ice did not overtop them.
On the trail to Potter Pass, older drift extends up to 7,500 feet, and at this altitude the trail crosses a distinct morainal ridge which is probably the crest of the highest lateral moraine on the north side of the lake. Northwest of Huntington Lake, on the small volcano called Black Point, granite boulders are within about 400 feet of the top, an altitude probably corresponding to the upper limit of the ice. The earlier glaciers did not overtop the ridge connecting Black Point and Kaiser Ridge. Farther east, the lower course of Bear Creek is entrenched in massive terraces of the older drift. Still farther east, in the lower valley of the North Fork of Big Creek, a large volume of morainal material forms broad terraces on both sides of the Creek. These terraces slope westward toward Huntington Lake, and diminish in height from nearly 100 feet to about 50 feet.
Near the mouth of the North Fork, the tunnel of the Southern California Edison Company enters the mountain at a slight angle to the valley side, and for 900 feet traverses older moraine, being heavily timbered in this treacherous material. The thickness of the moraine against the valley side is estimated at close to 100 feet.
Southwest of Huntington Lake, older drift is scattered over the narrow, nearly level spur on which the town of Big Creek (altitude 4,500 to 5,000 feet) is built. Boulders and cobbles derived from it are used extensively to line garden walks. The moraine can be traced from Shaver Crossing down the road to Power House No. 2.
DEPTH OF CANYON CUTTING SINCE EARLIER GLACIATION
In a few places, there is evidence that throws light on the question of how much canyon cutting has occurred since the earlier glaciers withdrew. One of these places is in the basin of Kaiser Creek, north of Kaiser Ridge, where older drift forms a discontinuous veneer over the undulating slopes on both sides of the creek. In this region the stream lies in a small rock gorge apparently cut since the earlier glaciation. The gorge ranges in depth from about 20 feet, south of Mount Tom, to over 50 feet at the place where the trail from Potter Pass to Daulton Ranger Station crosses the creek.
In the lower part of Chiquito Creek basin, the older drift mantles smoothly rounded, gentle slopes and flat benches on either side of the stream (page 48). Chiquito Creek itself flows through a gorge cut in this mature topography. The gorge is about 10 feet deep, just above Placer Ranger Station, and over 100 feet deep near the mouth of the creek. The gorge is interrupted at Logan Meadow, where, for a section, the creek has been prevented from deepening its channel due to the massiveness of the granite. Relationships typical of those found along the Chiquito Creek gorge are shown in figure 35.
With reference to the San Joaquin River, similar evidence was found in the vicinity of the mouth of Chiquito Creek. The lowest occurrence of older drift, in place, was found on the north side of the San Joaquin channel, at an altitude of 3,250 feet, that is, 300 feet above the river level. It would appear that at this point the maximum depth by which the river could have deepened its channel since the earlier ice withdrew is 300 feet.
In the San Joaquin Basin, as elsewhere in the Sierra Nevada during the Wisconsin stage of glaciation, the volume of ice was considerably smaller than in the earlier stage, and the ice-covered area was, therefore, much less extensive. The San Joaquin glacier system had, of course, the same general pattern as in the earlier stage, for it reoccupied most of the cirques and followed the same valleys and canyons, but it took the form of numerous discrete glaciers which became confluent only in part. Accordingly, large upland areas which were ice covered in the earlier glaciation remained bare throughout the Wisconsin stage (figs. 36, 37).
By far the greater part of the ice which formed in the San Joaquin Basin was again part of a bilobate system, and this character was the more pronounced because the ice was largely confined within the canyons or broad valleys. The trunk glacier in the main canyon, formed through union of the Middle Fork and South Fork glaciers, was only a feeble tongue reaching but 2 miles below the junction. The altitude at the terminus, the lowest point reached by the Wisconsin ice in this basin, was 3,400 feet. The maximum length of the San Joaquin glacier system, measured from Muir Pass at the head of the South Fork, was 47 miles: the length, measured along the Middle Fork, was 32 miles.
Some glaciers, which in the pre-Wisconsin stages were tributary to the San Joaquin glacier system, in the Wisconsin stage fell short of joining that system, and throughout their existence remained separate ice bodies or becanne confluent only with adjacent glaciers. This was the situation with the Granite Creek glacier, the Big Creek glacier system, and many smaller glaciers on Chiquito Ridge, Kaiser Ridge, and other ridges.
MIDDLE FORK GLACIER
Middle Fork glacier was a complexly branching body. The main ice stream, in Middle Fork Canyon, received tributaries from all of the important branch valleys occupied in the earlier glaciation, excepting Granite Creek. In their upper reaches (fig. 38), the branch glaciers were larrgely separated by long ridges of the cleaver type, many of them nunataks. Conspicuous among these ridges was the narrow crest of the Ritter Range, between the upper North Fork and the Middle Fork glaciers. At the south, the rather similar Silver Divide parted the sources of Fish Creek glacier from glaciers of the South Fork system. Downstream, the branch glaciers were channelized within the gorges into relatively narrow but deep ice streams. The lower courses of the North Fork, South Fork, and Fish Creek glaciers swept around and isolated several broad upland tracts which the earlier ice had overridden, for example that platform extending from the Granite Stairway to Lions Point. The ice reached a depth of more than 2,500 feet at the junction of the North and Middle Forks. Balloon Dome was a nunatak, the ice of this stage rising to a level of 1,500 feet above its base but never overwhelming the summit.
The North Fork glacier received a large branch from the valley of what is now the East Fork of Granite Creek. The East Fork glacier bifurcated, one very small lobe extending southward across a low divide into the Granite Creek basin, where, at Soldier Meadow, it just reached but failed to join the glacier of that basin. During deglaciation, the disappearance of this small lobe permitted the rearrangement of drainage whereby a stream previously tributary to the North Fork of the San Joaquin River was diverted across the low divide and became the present East Fork of Granite Creek.
SOUTH FORK GLACIER
The glacier system in the basin of South Fork was larger and more complex than that in the basin of Middle Fork. Its maze of ramifying sources was incompletely defined by the winding, branching crests of Mono Divide, Glacier Divide, Goddard Divide, LeConte Divide, the Silver Divide, and other ridges (fig. 39). Some of the small glaciers on the south side of the Silver Divide and on the north side of the Kaiser Ridge joined the South Fork system.
The trunk glacier, although the product of many large, convergent ice streams, was relatively unimpressive. For a number of miles it did occupy the full width of the broad upper valley of the South Fork (fig. 40), and below the junction of the Mono Creek branch the ice was more than 5 miles wide and 1,500 to 2,000 feet deep; but farther downstream it dwindled to a narrow ice tongue which, northeast of Hoffman Meadow, was entirely confined within the inner gorge, here only 1/2 to 1 mile wide and about 1,500 feet deep. At its junction with the Middle Fork glacier, the South Fork glacier had much the lesser volume of the two branches.
At Selden Pass, striae and chatter marks on the bedrock show that ice from the head of Bear Creek basin moved southward into the South Fork system. Evidently the ice in Bear Creek basin was much higher than that in the South Fork.
During deglaciation, the Mono Creek glacier, following its separation from the main trunk glacier in the valley of the South Fork, left a remarkable series of seven crescentic frontal moraines at the lower end of Vermilion Valley (fig. 41). These ridges enclose a 3-mile long meadow, and the swales between them also are occupied by narrow strips of meadowland. Traced up the south side of Vermilion Valley they unite into several straight lateral moraines extending for about 2 miles.
In investigating potential dam sites, the Southern California Edison Company in 1924 drilled a series of eight test holes in this area of frontal moraines. The line of holes apparently began near the axis of the valley and extended east-northeast in a nearly straight line across the remainder of the valley. The eight holes penetrated, respectively, 180, 116, 77, 74, 62, 25, 5, and 2 feet of unconsolidated material, including boulders, gravel, and sand, probably both glacial and glaciofluviatile material older than the Wisconsin as well as of Wisconsin age. The hole nearest the axis of the valley was still in unconsolidated material at the 180-foot depth (written communication, D. H. Redinger September 15, 1924).
Immediately east of Vermilion Valley, and at levels 1,500 feet or more above its floor, is another series of moraines, disposed in a fan shape. They converge eastward, and across the divide between Mono Creek and Bear Creek they unite to form lateral moraines on the north side of Bear Creek valley. These moraines graphically record the fact that the Bear Creek glacier, on rounding the great right-angled bend in its valley, at higher stages overrode the crest of Bear Ridge to the north and contributed ice to the Mono Creek glacier.
West of Vermilion Valley is a third cluster of moraines (fig. 42): a concentric system of large, curving ridges, the convex sides of which are directed northeastwardup the valley of Mono Creek rather than down it, as in the case of the much smaller Vermilion Valley moraines. These moraines are now deeply notched by Mono Creek (fig. 43). They are the right lateral moraines of the South Fork glacier, and mark the successive borders of the ice which, following the separation of the trunk glacier and the Mono Creek branch, for a time bulged a short distance into the newly evacuated lower Mono Creek valley (fig. 44).
GLACIERS ON KAISER RIDGE
Prominent and almost continuous lateral moraines define the upper levels of the South Fork trunk glacier. East of Hoffman Meadow are several parallel moraines with definite crests. The highest moraines, traced north-northwestward, end on a spur at the edge of the San Joaquin Canyon, at an altitude of 6,600 feet, east of the mouth of a hanging valley. These moraines in places follow ridges of granite, but on the whole they are laid irregularly cutting across the drainage lines and ridges at an angle. In several places an indistinct moraine was found just outside the main Wisconsin moraine, and in general parallel to it, suggesting the record of an early maximum of Wisconsin glaciation, similar to the record on both sides of the Little Yosemite Valley (Matthes, 1930a, p. 58-61).
At the junction of the Middle and South Forks, the uppermost lateral moraine on the north side of the South Fork is unmistakable although it is not strong. It meets the multiple lateral moraine of the Middle Fork at an altitude of 6,000 feet above Rattlesnake Lake.
Eastward-trending Kaiser Ridge presents an interesting contrast in that it has been severely glaciated on the north side and only mildly on the south side.
Glaciers of the south side were relatively small, separate ice bodies. One of the larger ones headed on Kaiser Peak, altitude 10,300 feet, and occupied the valley between Bear and Line Creeks. This glacier was 2-1/2 miles long and descended to 7,400 feet. Its lower positions are indicated by conspicuous loops of moraine, and similar loops define the limits of the smaller Deer Creek, Line Creek, and Home Camp Creek glaciers. Nellie Lake, which lies in a cirque without headwall, although surrounded by mountains of moderate declivity, is impounded by a strong moraine dam, outside of which, on somewhat lower ground, is another much larger and higher morainal embankment.
About 2 miles east of Kaiser Pass, a narrow ice tongue originating at about 10,000 feet descended low enough to coalesce, in part, with the Big Creek glacier. Its terminal portion pushed westward across a divide into the valley of the North Fork of Big Creek, which was ice free. This glacier reached a length of 3-1/2 miles and a lower limit of 7,700 feet. It left a complex of moraines, some of which border Badger Flats. Other moraines, including the right laterals of the Big Creek glacier, have effected the diversion of a stream in the upper valley of Big Creek to the drainage of the North Fork. The trail, which goes south from Badger Flats, passes through the part of the lower valley left streamless by this diversion.
Still farther east on Kaiser Ridge, broad shallow cirques at 10,000 to 10,500 feet contributed ice to the Big Creek glacier, by way of the valley of the East Fork.
On the north side of Kaiser Ridge lay a rank of glaciers that coalesced, along the crestal part of the range, into an almost continuous mantle of ice. At lower altitudes these glaciers, 2 to 4 miles in length, separated into individual lobes, which terminated in valleys on the upland, at altitudes of 7,400 to 4,100 feet. In the eastern part of the range, the glaciers joined the South Fork trunk glacier, at altitudes of 7,500 to 8,500 feet. The lateral moraines of the trunk glacier cut straight across the lower valleys of Kaiser Ridge, marking the well-defined level at which the lateral moraines of the tributary glaciers on Kaiser Ridge abruptly terminate.
The largest glacier on the north side of Kaiser Ridge occupied Kaiser Creek valley. It headed in a series of cirques stretching for 5 miles along the crest of Kaiser Ridge, south of Kaiser Peak Meadows. The ice descended to an altitude of 7,100 feet, about 3/4 mile below Sample Meadow. This glacier left an exceptionally fine morainic record, its recessional moraines marking stages not only in the shrinkage of the confluent ice body but also in the final dwindling of the little individual glaciers into which it eventually separated. That the Kaiser Creek glacier at one time was voluminous enough to spill over the saddle east of Sample Meadow, and thus joined the San Joaquin trunk glacier, is attested by the prominent ridges of moraine that descend from the hill to the southeast of the saddle.
Outside the prominent outer morainic loop of the Kaiser Creek glacier is another loop consisting of isolated boulders 50 to 100 feet apart. This loop appears to be an older moraine from which the finer material has been washed away. Yet this moraine is not comparable in age to the moraines of the earlier glacial stage, for its boulders rest on ground resembling that occupied by the younger moraine, that is, ground which has not disintegrated deeply enough to produce pinnacles and crags, but which still shows the smoothing effects of ice. This moraine therefore properly may be regarded as representing early Wisconsin time. It is analagous to similar moraines noted in various places in the Yosemite region.
At Twin Lakes, east of Kaiser Peak, some of the granite erratics of the Wisconsin stage that rest on limestone bedrock have become perched on pedestals, due to relatively rapid reduction of the surface of the limestone by solution and frost action (fig. 45). One boulder 5 feet high and 7 feet long stands on an 8-foot pedestal.
GRANITE CREEK GLACIER
The glacier which occupied the Granite Creek basin during the Wisconsin stage, and which throughout its existence remained separate from the Middle Fork glacier, was fed from sources mostly situated along the east side of the crest extending southward from Triple Divide Peak, at altitudes of 9,000 to 11,000 feet. These sources formed a continuous gathering field which from north to south was almost 8 miles across. The lower part of the glacier was a blunt lobe which lay about a mile southeast of the Clover Meadow Ranger Station, at an altitude of 6,900 feet. From its source on Triple Divide Peak to this terminus the glacier was 9 miles long. Multiple-crested moraines of this glacier are prominent south of Clover Meadow and in the vicinity of Soldier Meadow.
GLACIERS IN CHIQUITO CREEK BASIN
As in the earlier glaciation, Chiquito Ridge developed glaciers only on its northeast side, where they were small, separate ice bodies. Several of these, all cirque glaciers, were clustered on the east and northeast sides of Shuteye Peak, altitude 8,358 feet; three additional slightly larger glaciers, each about 2 miles long, formed farther to the northwest at altitudes of about 8,000 feet, between Little Shuteye Peak and Texas Flat. The lower ends of these glaciers lay at altitudes of 6,850 to 5,700 feet.
Small glaciers also formed in the extreme head of the basin, on Redtop Mountain and Sing Peak, at altitudes of about 10,000 feet; and ice confluent with the Merced glacier flowed 1 or 2 miles into Chiquito Creek basin, where it left beautiful loops of moraine just south of Chiquito Pass. These moraines are crossed by the trail through the pass.
GLACIERS IN THE BIG CREEK BASIN
In the Wisconsin stage, glaciers again descended the tributary valleys of Big Creek, but the trunk glacier they produced was small and remained separate from the little glaciers on the central and western parts of Kaiser Ridge. In fact, the glacier in the branch valley of Tamarack Creek failed to unite with its neighbor in the East and South Fork branches of Big Creek valley, though at their sources the ice bodies in places were confluent. The Tamarack Creek glacier was 5 miles long and descended to an altitude of 7,400 feet. The Big Creek glacier was over 10 miles long, following the East Fork, and descended to 6,900 feet. Its terminus was approximately in the middle of Huntington Lake.
In the headwater region of these glaciers, a number of hills and ridges over 9,500 feet high, including Black Peak (fig. 47), were nunataks. Here the upland topography has been only slightly modified by glaciation, but it is littered with drift. Long Meadow is truly a "moraine meadow" and with its many scattered granite blocks it presents a peculiar aspect (figs. 47, 48). Moraine ridges, 10 to 20 feet high, are locally conspicuous.
The lower limits of the Big Creek and Tamarack Creek glaciers are marked by conspicuous moraines. The right lateral moraines of the Big Creek Glacier extend westward from the base of Bear Butte. Near Huntington Lake they deploy northward to the mouth of the North Fork of Big Creek, then again run westward as low, rock-crowned embankments along the north shore of the lake. They decline in height very gradually to a point just west of Bear Creek, where they disappear beneath the lake. The left lateral moraines are massive embankments which flank the north base of Chinese Peak. They continue northwestward to the south shore of the lake, obstructing southward drainage and giving rise to a large wet meadow. Finally they dip into the lake at the end of a rocky promontory about 1 mile west of the mouth of Big Creek. Small rocky islands near the lake shore carry glacial boulders, and a long line of boulders protruding from the lake near its end, marks the crest of a drowned moraine.
Last Updated: 27-Jul-2009