ABSTRACT Shorelines formed by terminal lakes record past changes in regional moisture budgets. In the western Great Basin of North America, winter precipitation accounts for nearly half of the annual total and is well correlated with northeast Pacific storm track activity and moisture transport. We evaluated these relationships and found that historical precipitation between 1910 and 2012 was better correlated to moisture transport (0.78, p < 0.01) than to storm track activity (0.54, p < 0.01) because moisture transport better captures dynamics associated with the Sierra Nevada rain shadow. We derived modern analogs of enhanced and reduced storm track activity and moisture transport from reanalysis products and used associated winter precipitation anomalies with these analogs as inputs to a coupled water balance and lake evaporation model of the Walker Lake basin. Simulated lake-level responses were compared with a radiocarbon-dated lakeshore chronology spanning the past 3700 yr. Wet analogs developed from winters in the 90th and 75th percentiles for storminess and moisture transport produced lake levels that exceeded estimated late Holocene highstands by 50 m. Dry analogs (10th and 25th percentiles) produced lake levels corresponding to Medieval megadrought lowstands. The twentieth century is shown to be as wet as any century in the past 3700 yr. Our results demonstrate the sensitivity of terminal lakes to winter season circulations and highlight the value of using moisture transport as a predictor of cool season precipitation and to evaluate how past or future changes in regional circulations will influence the water balance of dryland regions.

ABSTRACT The Searles Lake Formation in Searles Valley, southeastern California, represents deposition of the paleo–Owens River into a Pleistocene and Holocene pluvial terminal lake. A prior 32–10 ka estimated age for the upper part of the Searles Lake Formation relied on uncalibrated, conventional radiocarbon dates. We present accelerator mass spectrometer radiocarbon dates that indicate the base of the Searles Lake Formation at the Poison Canyon type section is 46 ka. That age is consistent with paleomagnetic data at Poison Canyon and the Tire Farm locality, which record high-latitude Southern Hemisphere virtual geomagnetic poles that we assign to the 41 ka Laschamp excursion. The presence of Searles Lake at 46–43 ka also is consistent with a Pacific storm track that extended south of 37.5°N at that time. At the head of Salt Wells Valley–Poison Canyon, sediments that we interpret as a Searles Lake highstand were radiocarbon dated at 14.1 ka.

ABSTRACT The Carrizo Plain, the only closed basin in California’s Southern Coast Ranges, preserves landforms and deposits that record both climate change and tectonic activity. An extensive system of clay dunes documents the elevations of late Pleistocene and Holocene pans. Clay dune elevations, drowned shorelines, eroded anticlinal ridges, and zones of perturbed soil chemistry provide evidence of two lake levels higher than today’s (currently 581 m above sea level [masl]), one at ~591 masl at ca. 20 ka and another at ~585 masl that existed at ca. 10 ka, based on optically stimulated luminescence (OSL) dates on clay dune sediment. Two cores from the abandoned floor of the lake provide additional evidence of a long-lived lake in the Carrizo Plain during the late Pleistocene. The longer of the two cores (~42 m) was sampled for palynology, environmental magnetism, and scanning electron microscope–petrography. The magnetic susceptibility signal contains two notable features corresponding to sedimentary materials consistent with reducing conditions. The higher of these features occurs near the surface, and the lower occurs at ~18 m depth. A 14 C date on charcoal from the upper reduced zone places the top of this zone at no older than 22.6–20.9 cal ka. This date is consistent with the OSL date on geomorphic features associated with a highstand above ~591 masl. Assuming that reducing conditions correspond to at least a few meters’ depth of relatively fresh water, the new 14 C date suggests that the upper reduced zone represents a marine isotope stage (MIS) 2 pluvial maximum lake in the Carrizo Plain. Pollen and ostracodes from the reduced sediments indicate a wetter and cooler climate than today. These conditions would have been capable of sustaining a lake with water much less saline than that of the modern lake. The timing of the oldest documented highstand (no later than 20 ka) is consistent with a modified jet stream migration model and is not consistent with a tropical incursion model. Northeast-to-southwest asymmetry across the lake floor may be consistent with southwestward tilting driven by Coast Range shortening normal to the San Andreas fault, as is seen throughout the region.

ABSTRACT The Uinta Basin of eastern Utah is an intermontane basin that contains an ~2-km-thick succession of mostly carbonate-rich mudrock assigned to the Eocene Green River Formation. In the southwest part of the basin, along Nine Mile Canyon and its tributary canyons, the middle member of the Green River Formation contains numerous interbedded sand bodies. Previous researchers have interpreted these sand bodies variably as lacustrine deltaic mouth bars, terminal fluvial distributary bars, and various types of fluvial (delta plain/floodplain/braid plain) bar. Using some modern western U.S. lakes as partial analogues, and taking into account the overall lacustrine basin context of a widely fluctuating, wave-influenced, alkaline-lake shoreline, we again interpret many of the sand bodies to be fluvial in origin. Several sand bodies both truncate and are capped by brown to red-maroon and variegated weak to noncalcareous mudstone with root and desiccation structures, indicating terrestrial deposition well away from the lake shoreline. Others display steep cutbanks from which noncalcareous, inclined heterolithic stratification laterally accreted as fluvial side bars. Utilizing helicopter-based light detection and ranging (LiDAR) data, we investigated additional sand bodies that may be better examples of deltaic mouth bars. In contrast to the more commonly documented highstand progradational mouth bars of marine and open lake settings, these sand bodies are interpreted to have originated as late-lowstand or transgressive system tract fluvial channels that were then flooded and modified by waves following lake transgression. These examples illustrate that any large-scale sandy bed form present in the general vicinity of a closed basin’s fluctuating lake shore may be expected to have formed under more than one set of environmental conditions. A revised set of guidelines is therefore presented to aid in the interpretation of lacustrine deltaic mouth bars.