After the materials are transported by the erosional agent, they are eventually deposited at a new location. Deposition is the third geomorphic process. These depositional materials commonly form distinct landforms that are attributed to a particular geomorphic agent. These landforms can then be identified as fluvial (running water), glacial (glacier), colluvial (gravity), periglacial (ground ice), aeolian (wind), marine (waves, tides, and currents), or biological (organisms) in origin. They too can then yield climatic information, as these depositional agents vary with climate.
Depositional landforms commonly can be identified by their distinctive shapes, but landforms deposited many years ago may have been worn down by weathering processes and lost their once-distinct appearance. It is still possible to identify these landforms as to their depositional agent based on knowledge of how various geomorphic agents shape and sort materials. Table 2.2 lists the characteristic shapes and degrees of sorting of sediments by various agents. This table serves as a guide to identifying depositional landforms in the White-Inyo Range. It can be seen from this chart that glacial clasts (particles) are commonly subangular and poorly sorted, in contrast to fluvial clasts, which are rounded and well sorted. (These differences are due to the densities and velocities of the fluids [agents], among other factors.) Thus, if we find a deposit with no characteristic morphology on a ridgetop, valley floor, or intermediate slope, we can commonly identify its agent of deposition. Early Quaternary high-altitude ridgerop (interfluve) deposits on Cottonwood Plateau (Fig. 2.4) and Chiatovich Flats (Fig. 2.5) have been identified as glacial in origin by sediment analyses, as surface expression of glacial landforms is lacking.
Geomorphologists have long been interested in the presence of apparent high-altitude planation surfaces at crestal and mid-elevation positions in many mountain ranges (see Fig. 2.5). These surfaces are commonly present on fault-block mountains and have been hypothesized to have been eroded in valley floor positions, then uplifted with the range. They are typically mantled with depositional material. It is possible to identify multiple planation surfaces at several distinct elevations in a particular mountain range. If these surfaces were formed at valley bottom locations, determination of their time of formation could shed light on rates of tectonic activity for a range (e.g., when was the range uplifted?) (Curry, 1984). However, many workers believe that these high-altitude surfaces were simply eroded in place by various agents, especially frost action (ground ice); as such, they have been referred to as cryoplanation surfaces. A third group of scientists believe that these surfaces were very likely the result of both past lower-elevation and present higher-elevation processes.
High-altitude erosion surfaces are distinct in the White Mountains. The best example is Pellisier Flats, which extends from an elevation of 12,400 ft (3,775 m), near Mt. Hogue at the south, to 13,400 ft (4,080 m) at The Jumpoff, just south
of Boundary and Montgomery peaks to the north. What appears to be an extremely flat surface from distant positions to the west or east of the range is actually a gently rolling surface with small, residual bedrock outcrops (inselbergs, tors, and monadnocks) (Fig. 2.6). The surface is mantled with frost-shattered debris and is presently a periglacial landscape. Both active and relict patterned ground occur here (Mitchell, LaMarche, and Lloyd, 1966; Elliott-Fisk, 1987; Mahacek-King et al., 1987) and dominate the surficial geology of other high plateaus in the range.
Ongoing research focuses on how extensively these plateaus were covered with glacial ice, which requires either the formation of an ice cap, under present topographic constraints, or the presence of valley glaciers prior to tectonic uplift and an episode of major stream incision (valley formation). Many of the high plateau surfaces are mantled by glacial deposits that have been somewhat reworked by frost action and fluvial processes (Elliott-Fisk, 1987). Chiatovich Flats (10,200–11,600 ft, or 3,130–3,560 m, elevation) and the Cottonwood Plateau (11,200–12,000 ft, or 3,435–3,680 m, elevation) are the best examples. Other surfaces are mantled by rock glaciers (such as the North Fork Perry Aiken Creek, Fig. 2.7) and felsenmeer (i.e., frost-shattered boulder fields; see Figs. 2.1 and 2.6).
Geomorphologists have long debated whether felsenmeer indicates the absence of glaciation. This is a difficult question because our knowledge of high-altitude weather-
ing rates is poor. The thin ice cover of a cold-based glacier (frozen to the surface) may allow the preservation of felsenmeer. The plateau between Mt. Barcroft and White Mountain Peak apparently had such an ice cover in the past, as large, frost-shattered blocks on the plateau above the cirques of the North and South Forks of McAfee Creek show surface polish and abrasion, indicating that this area was in the zone of accumulation of a former glacier (Elliott-Fisk, 1987). The same or an adjacent glacier may have deposited the granodiorite erratics on the dolomite surface of the Cottonwood Plateau to the south (see Fig. 2.4). If the time of formation of these glaciers can be deduced, the rate of high-altitude weathering since its disintegration can be calculated.
The tectonic activity of the earth can be characterized as an internal geomorphic process. Displaced, faulted, and warped landforms attest to local tectonic activity. Good examples of these exist along the western and eastern escarpments of the White-Inyo Range in the form of displaced alluvial fan (Fig. 2.8) and lake bed materials.
Alluvial fans are triangular or cone-shaped masses of debris at the base of a mountain front (see Fig. 2.2). Deposition of alluvial and colluvial material results when the lower gradient and wider channel of the valley floor are encountered as the material is transported down the mountain flanks. The velocity of the fluid drops, causing
the deposition of these materials. Streams spread out as distributaries at this point, instead of coming together in the form of tributaries to a main stream channel, as they do in the drainage basin above.
As one ascends the stream canyons at the apex (head) of these alluvial fans, older fan materials (fanglomerates) may be seen perched on the walls many meters above the present fan surface (as along Indian Creek, Milner Creek, and Black Canyon). It is also possible to find an older fan apex at a higher elevation back in the mountain front (as at Jeffrey Mine Canyon on the west slope of the White Mountains). If these materials can be dated, the amount of tectonic uplift can be calculated. Unfortunately, these deposits are difficult to date, as they are usually beyond the age range of radiocarbon or lack organic materials necessary for radiocarbon dating. However, along Black Canyon in the southwestern White Mountains (see Fig. 2.8), a volcanic deposit is interbedded with fanglomerate. This material is tephra (air-filled lapilli and ash) from the catastrophic eruption of the Long Valley caldera and is referred to as the Bishop Tuff (volcanic ash) (Bateman, 1965). It has been dated by uranium fission and other techniques, with the best estimate of its age currently at 0.79 Ma (millions of years before present). This deposit is present in Black Canyon 490 ft (150 m) above the valley floor, attesting to 7.6 in (19 cm) of uplift per 1,000 years.
Near the Westgard Pass road at the Waucoba Embayment of the western front of the White-Inyo Range, a series of lake beds (the Waucoba Lake beds) is exposed.
Walcott (1897) speculated that these lake deposits have been uplifted 3,300 ft (1,000 m) above the valley floor. Although intensive studies of these deposits have not yet been conducted, their age is estimated at 3 million years, suggesting an uplift rate of 13 in (33 cm) per 1,000 years.
The relatively slow tectonic uplift of the range may not seem important in reference to our short lifetimes, but some tectonic activity, generating earthquakes and displacement along fault lines, can be abrupt. Escarpments along fault lines cutting through alluvial fans suggest rapid vertical displacements of several meters. Further research needs to focus on dating this tectonic activity, which can be accomplished through studies of soil formation on the fans. The presence of ash from the Mono and Inyo craters interbedded with uplifted fan sequences and other deposits (Fig. 2.9) suggests tectonic disturbance in the last 5,000 years (Mahacek-King et al., 1987; Mahacek-King et al., 1988). It is now well known that the entire region is tectonically, and hence geomorphically, very active, as has been shown by intensive studies in the Long Valley caldera region and along the White Mountains fault zone, and by historical records of earthquake occurrence. It is believed by some workers (Curry, 1984) that this tectonic activity is accompanied by volcanism and basin formation and is migrating north from the Owens Valley (which witnessed a catastrophic eruption about 790,000 ka (thousands of years before the present) to the Mono Basin (which is still volcanically active) and the Bridgeport basin. This may be related to major plate rifting along the axis of the Gulf of California and to crustal extension.
A wide variety of materials is available for landform generation in the White-Inyo Range. All three basic rock classes (igneous, metamorphic, and sedimentary) are present and range from Precambrian to Quaternary in age (see Chapter 3). The mineralogy and petrology of these rocks vary, with some more susceptible to jointing, chemical weathering, and other processes. Thus, some types of landforms tend to be associated with distinct rock formations. For example, the Campito Formation (especially the Andrews Mountain Member), a sandstone or quartzite, is very susceptible to frost action, resulting in the formation of angular felsenmeer seen as stone stripes on slopes along White Mountain Road. Bateman (1965) contrasts this with the Montenegro Member shale, which forms slabs and breaks down rapidly to clay-rich soils. Differences in patterned ground derived from metamorphic and granitic materials are apparent at high elevations.
The White-Inyo Range is largely lacking in organic-rich deposits and landforms, in the form of either peat or fossilized organic remains. This is most likely due to the present aridity of the range and the lack of topographic depressions along the steep mountain flanks. Organic-rich deposits may compose distinct landforms, but they possess other advantages in that they are a superb source of material for the study of fossil plant and animal communities and for dating of geomorphic events (see Fig. 2.9). Recently, turf and earth hummocks have been found in the Alpine Zone of Pellisier Flats and register geomorphic change with the deposition of volcanic tephra and changing hydrology of the site (Mahacek-King et al., 1987). The arid climates of the range have allowed woodrat middens to be preserved in a diversity
of environments. Analysis of plant macrofossils from these middens is providing valuable information on the late Quaternary geologic and climatic history of the range (Jennings, 1988; Jennings et al., 1989).
Reference has been made throughout this section to the role of time in the control of landform development. If we think of the White-Inyo Range as a dynamic mountain system that is continuing to evolve, we can ask not only what landforms are developing now, but which ones were formed in the past, when they were formed, and what this tells us about the evolution of the range.
The geologic evolution of the range is discussed in Chapter 3 of this book. However, in a general sense, it can be stated that all landforms visible today are the
products of late Cenozoic processes. We can imagine many of the high peaks (such as White Mountain Peak) forming over millions of years through weathering and erosion. It is very likely that the peak was always exposed to the subaerial environment, perhaps a nunatak above a hypothetical White Mountain ice cap. Other landforms are more recent, forming with the glaciation of the range or by recent fluvial activity.