Abstract Geomorphology, the study of landforms and the processes that shape them, emerged in its modern form in the mid-twentieth century and continues to change. Its practice, however, derives from the convergence of discrete foundations in the Earth, water and applied sciences over the past 400 years, underpinned by advances in analysis and technology. The Earth-science foundation was built as early geologists sought to explain landforms as expressions of underlying rocks or as surrogates for vanished stratigraphies. This approach, more speculative than definitive, rarely explained the processes at work. The water and applied sciences were more discerning but only slowly came to be integrated into morphodynamic explanations. All three foundations, initially vague on time and space, emerged during the Scientific Revolution of the seventeenth century and were refined during the agrarian and industrial revolutions of the eighteenth and nineteenth centuries, before converging into modern practice during the electronic age of the twentieth century.

Abstract Scientific investigations of Pleistocene pluvial lakes in the American West occurred in five phases. The pioneer phase prior to 1870 saw former lakes identified by missionary priests, fur trappers, military expeditions and railroad surveyors. The classic phase, between 1870 and 1920, linked initially with independent surveys and, after 1879, with the United States Geological Survey and with irrigation and mining ventures, saw most lakes identified and described by such worthies as Gilbert, Russell, Gale, Waring and Thompson. A consolidation phase from 1920 to 1955 provided synthesis and new data but, in the absence of age controls, saw much speculation about temporal links between pluvial lakes, glacial stages, and climate forcing. The initial dating phase between 1955 and 1980 saw radiocarbon dating applied to late Pleistocene lakes and their Holocene relics and successors. The integrative phase since 1980, supported by enhanced field, remote sensing, laboratory and dating techniques, has seen an array of issues involving pluvial lakes linked to changes in regional ecology and global climate. In the above sequence, progress from one phase to the next reflected changes in the intellectual climate and advances in scientific methods. Today, we reflect on the episodic but cumulative increase in knowledge about late Pleistocene pluvial lakes, especially for Lake Bonneville, Lake Lahontan and the eastern California lake cascade. The record of earlier Pleistocene lakes, in some cases successors to Miocene and Pliocene lakes, is less certain because of deformation and erosion or burial. Continuing challenges involve evaluation of the Pleistocene lake record as a whole in the context of late Cenozoic tectonic and climate change, and of contemporary environmental and water-resource issues.

Owens Lake has existed for most of the past 800,000 yr, but the sequence of interconnected lakes and streams of which it was often part, the Owens River cascade, last flourished during late Pleistocene time. A fluctuating, increasingly saline, terminal lake survived into the late Holocene until upstream water diversions to the Los Angeles Aqueduct began in 1913. Shoreline fragments and beach stratigraphy indicate that the lake reached its highest late Pleistocene level around 23.5 ka, during the Last Glacial Maximum, when it was fed by meltwaters from Sierra Nevada glaciers and spilled southward to Searles Lake and beyond. The lake then fell to relatively low levels after 16.5 ka before experiencing terminal Pleistocene oscillations related to hydroclimatic forcing, which involved changing regional precipitation regimes rather than major inputs from Sierra Nevada glaciers. Two major transgressions occurred. The first culminated around 14.3 ka and was probably related to a cooler, wetter regional climate. The second culminated around 12.8 ka and was linked to the earlier wetter phase of the Younger Dryas cold event. However, the high late Pleistocene shoreline is deformed, and the highest beach ranges in elevation from 1140 m to 1167 m above sea level. If the terminal Pleistocene lake overflowed, as suggested here, then its outlet has also been raised since 12.8 ka. This deformation appears to have involved uplift of the Coso Range magmatic complex relative to subsidence and faulting within the Owens Lake graben between the Sierra Nevada and Inyo Mountains frontal faults. Such deformation confounds simple hydroclimatic explanations of lake behavior and must be incorporated into models that seek to interpret the changing form and geochemistry of Owens Lake and the frequency of its spillage southward to Searles Lake.

Lakes in one form or another have characterized the western Mojave Desert since at least Miocene time. The most recent of these, Lake Thompson, developed in the late Pleistocene, when it covered as much as 950 km 2 and rose to at least 710 m above sea level. During Holocene time, the lake desiccated, and is now represented by Rogers, Rosamond, and Buckhorn dry lakes, which may flood up to 200 km 2 during unusually wet phases. The spatial dimensions of the former lake are defined by modest geomorphic and lithostratigraphic units, mostly exposed lake beds and beach ridges interbedded with and later mantled by fluvial and eolian deposits. The lake's temporal devolution is revealed by four cores, and ages are constrained by accelerator mass spectrometry 14 C dating of organic sediment. These cores show a deep perennial lake from before 36 ka to at least 34 ka, a shallow but variable perennial lake from before 26 ka to 21 ka, followed by lowering and at least partial exposure of the lake floor to deflation and alluviation. A shallow perennial lake returned during the terminal Pleistocene, from around 16.2 ka to at least 12.6 ka, forming distinctive beach ridges beyond the margins of the present dry lakes, and it may have reappeared in the early Holocene. During subsequent Holocene desiccation, lake segmentation occurred as waves and currents generated lower sequences of beach ridges around contracting lakes. These ridges became mantled with eolian sand, but, as fluvial sediment inputs diminished with increasing aridity, these dunes were degraded, and their roots survive today as indurated yardangs.

Abstract Clarence Edward Dutton (1841–1912) was one of several scientists who laid the foundations for modern geology from their work in North America during the late nineteenth century. Dutton was a career soldier who fought in the American Civil War and remained with the US Army Ordnance Corps to his retirement in 1901. Despite military obligations, Dutton developed a profound interest in geology and, on secondment first to the Powell Survey and later to the fledgling US Geological Survey, made important contributions to volcanic geology, seismology and physical geology. His lifelong fascination with volcanism led to improved understanding of the volcanic geology of the American West, Hawaii, and Central America. This work linked naturally with the emerging science of seismology, as reflected in his study of the 1886 earthquake in Charleston, South Carolina, and he is often credited with introducing the ‘new seismology’ to American scientific audiences. Awareness of volcanic and seismic hazards in turn led him to caution against a proposed sea-level canal across the Nicaraguan isthmus. His contributions to physical geology are most evident in several reports on the American West, notably the Report on the Geology of the High Plateaus of Utah (1880), the Tertiary History of the Grand Cañon District (1882), and Mount Taylor and the Zuni Plateau (1885). These reports, presented in colourful prose, reveal both the author's scientific acumen and his aesthetic appreciation of nature. Whereas most of Dutton's work must now be placed in its historical context, in his recognition of isostasy, a term he coined in 1882 to reflect the debate then raging concerning Earth's crustal behaviour, his ideas were remarkably prescient. Dutton's interest in isostasy derived in part from his studies of volcanic geology, seismology, and crustal behaviour, and in part from his fieldwork in the American West. Initially, however, it was Dutton's description of the great denudation of the Colorado Plateau, rather than any isostatic implications, that influenced geomorphology during the earlier twentienth century, dominated as it was by Davis' cycle of erosion. The subsequent demise of Davisian geomorphology, and the ensuing quest for alternative models, led to a reawakening of interest in isostasy as a concept basic to the explanation of Earth's surface features. Somewhat belatedly, Dutton's concept of isostasy is once again at the centre of debate regarding denudation and crustal behaviour. Wherever these debates focus, they confront a problem fundamental to geology, geodesy and geophysics, namely the extent to which the Earth's present relief reflects a quest for balance between the subsurface forces generating uplift, subsidence and mass transfers at depth, and the climate-induced processes responsible for denudation and mass transfers of rock waste across the surface. Dutton's probing of isostasy predated modern debate in geomorphology by more than a century.

Abstract Extensive coastal dunes rise southward from the Santa Maria Valley to the Point Sal Ridge, south-central California. In Mussel Rock ravine and elsewhere, eolian sands occur in association with fluvial deposits. Radiocarbon ages and correlative deposits in nearby areas indicate a sequence of events postdating marine-terrace deposits of oxygen isotope stage 5. Dissected paleodunes ( Qe ,), probably related to stage 4, are overlain by mostly sandy fluvial deposits ( Qf ) whose higher units yield 14 C ages in the 30- to 23-ka range. Transverse paleodunes ( Qe 2 ) began to form after 26 ka, as sea level fell during the transition from stage 3 to stage 2, and probably continued to accumulate westward during stage 2. Parabolic dunes ( Qe 3 ) formed from new and reactivated sand masses during the Flandrian transgression and were stabilized before 3 ka. Lobate dunes ( Qe 4 ) subsequently formed and the presently active transverse dunes ( Qe 5 ) have developed within the past 200 years. The chronology revealed near Point Sal may provide a valuable time frame for coastal-dune development elsewhere in California. The investigation indicates, for example, that extensive transverse dunes form during periods of sediment abundance, ideally when sea level falls and large quantities of sand are exposed on emergent continental shelves, but also when stabilized dunes are reactivated by environmental changes, including human land use. Parabolic dunes develop during periods of sediment deficiency—for example, as sea level stabilizes following a marine transgression.