Lake Lahontan Research Articles

A 14,100 cal B. P. Rocky Mountain locust cache from Winnemucca Lake, Pershing County, Nevada

The remains of approximately 1000 (MNI) Rocky Mountain locusts (Melanoplus spretus) from an archaeological cache pit in Crypt Cave, Winnemucca (dry) Lake, Nevada, date to between 14,305–14,067 calendar years before present (95.4 % confidence; 12,238 ± 18 14C yrs. B.P.). The age of this western Great Basin occupation along the shoreline of Lake Lahontan is consistent with occupation of several other Western North American terminal Pleistocene sites dating prior to 14,000 cal. B.P., including distinctive petroglyphs on the western shore of Winnemucca Lake dating as early as 14,800–13,200 cal. B.P.

Population genomic analysis of the Speckled Dace species complex identifies three distinct lineages in California

AbstractObjectiveSpeckled Dace Rhinichthys osculus is small cyprinoid fish that is widespread in western North America. In California and elsewhere it is currently treated as a single species with multiple subspecies, many undescribed. However, these subspecies may represent evolutionary lineages that are cryptic species because they cannot be distinguished using standard morphometric techniques. In this study, we attempt to determine evolutionary lineages within California populations of Speckled Dace using the population genetic and genomic information.MethodsWe used restriction site‐associated DNA sequencing to extract thousands of single‐nucleotide polymorphisms across the genome to identify genetic differences among all the samples from 38 locations in the western USA, with a focus on California. We performed principal component analysis, admixture analysis, estimated pairwise values of the genetic differentiation index FST, and constructed molecular phylogenies to characterize population genetic and phylogenetic relationships among sampled Speckled Dace populations.ResultOur analyses detected three major lineages of Speckled Dace in California that align with geography: (1) Sacramento River, central California coast, Klamath River, and Warner Basin; (2) Death Valley and Lahontan Basin; and (3) Santa Ana River basin, in southern California. These lineages fit well with the geologic history of California, which has promoted long isolation of populations of Speckled Dace and other fishes.ConclusionThe presence of distinct evolutionary lineages indicates that Speckled Dace in California should be managed with distinct population segments to preserve within‐species diversity. This study highlights the importance of genetic analyses for conservation and management of freshwater fishes.

Capturing the Void: Michael Light’s Aerial Photographs of the American West

In 2017 and 2018, the California-based photographer Michael Light went to the Great Basin, allegedly one of the emptiest places left in the continental United States, in search of the void. He returned with striking and aesthetically pleasing images of a desert that is far from empty. Working collaboratively with his colleagues at Radius Books, Light realized the series and photobook Lake Lahontan / Lake Bonneville (2019). In this work, Light employs the unique combination of aerial perspective and photographic abstraction to capture images of the Great Basin that challenge our perception of empty spaces, the desert, and the American West. Light’s images emphasize the paradoxical effect of humans on the environment while leaving space for interpretation. The work opens the viewer to larger questions about the impact all humans have on the earth, inevitably prompting viewers to recognize their own role in the process.

Complex Holocene Fault Ruptures on the Warm Springs Valley Fault in the Northern Walker Lane, Nevada–Northern California

ABSTRACTThe Warm Spring Valley fault is a right-lateral strike-slip fault situated in the northern Walker Lane—a region of distributed deformation that accommodates ~15% of the dextral shear between the North American and the Pacific plates. We assess the Holocene slip history through new mapping for the entire fault and a paleoseismic trenching investigation for the northern section of the fault. The fault is expressed in Holocene deposits for a minimum of 80 km and upward of 96 km, encompassing a wide deformation zone (~0.5–2 km) characterized by short discontinuous fault scarps in young alluvial deposits, stepping and anastomosing fault strands, pop-up features, linear drainages, and sag ponds. Trenching on the northern section of the fault reveals evidence for at least two and possibly three surface-rupturing events since 15.8 ± 1.3 ka, matching the timing of the Seehoo highstand of Lake Lahontan. Earthquakes are broadly constrained between 16.4 and 9.2 ka, a possible event between 9.0 and 6.4 ka, and an event between 3.5 and 0.1 ka, determined based on stratigraphic relationships and radiocarbon and optically stimulated luminescence geochronology. The ages of all three earthquakes provide a recurrence interval of ~5.5 ± 1.6 ka for the fault. The earthquake timing overlaps with trenching results from the southern section of the fault, suggesting that full-length fault ruptures generating Mw 7.3–7.4 earthquakes are possible. Post-Lake Lahontan sand dunes are faulted in the Honey Lake basin along with pluvial lake deposits next to Honey Lake, providing supportive evidence for one or multiple Holocene earthquakes. Faults range in orientation from 270° to 360° and match the orientations of shears in clay model experiments suggesting that fault ruptures on the Warm Springs Valley fault are complex, similar to complex historical earthquakes, and consistent with youthful fault development in the northern Walker Lane.

Lacustrine carbonate tufa facies of Winnemucca Dry Lake Basin, Nevada, U.S.A.

ABSTRACT Lacustrine carbonate tufa deposits are common in present-day lakes and dry pans of the western United States, and large-scale deposits (> 100 m high) are found throughout the subbasins of Pleistocene Lake Lahontan. This study presents a depositional model for very well exposed tufa in Winnemucca Dry Lake, a subbasin of Lake Lahontan, that incorporates new observations of tufa growth over length scales of 10–4–102 m. Tufa depositional facies are defined on the basis of outcrop morphology and texture. Deposits were mapped using satellite imagery and field observations. Tufa facies and volumes were quantified for seven tufa exposures across the basin using digital outcrop and elevation models from aerial images acquired from a small uncrewed aerial system (sUAS). Tufa thin sections were examined using transmitted-light petrography and scanning electron microscopy and combined with measurements of porosity and permeability to define small-scale facies characteristics. Both porosity and permeability are highly variable across textures; average values for both (ϕ = 29%, k = 5.5 D) indicate that all tufa types may exhibit excellent reservoir properties. The age and distribution of these facies across the basin are directly linked to hydroclimate and variations in lake level. The most important controls on tufa distribution at the basin scale are basin hydrology and pathways of groundwater inflow. Groundwater flow into the basin is largely concentrated along the western flexural margin along the contact between volcanic and volcaniclastic bedrock and alluvial sediments, rather than concentrated along the border fault margin, in contrast to other models which predict strong fault control of tufa occurrence. Microbially influenced tufa textures and morphologies are the most volumetrically significant tufas in the basin, composing between 77% and 100% of tufa volume at individual exposures; these are inferred to form during times when lake waters were warmer and levels higher, while physico-chemical processes dominate during early tufa formation, and generally in colder waters and under conditions of lower lake level. Deposition of tufas is a result of combined physical, chemical, and biological factors that are directly related to the basin geology and hydroclimate; however, the importance of each controlling factor is highly variable both spatially and temporally, complicating the development of effective and predictive depositional models. This case study describes tufa deposition intrinsically linked to basinal hydroclimatic histories, and understanding these relationships may assist in predicting volumes, physical properties, and stacking patterns of petroleum reservoir facies in lacustrine basins.

Constraints on mantle viscosity and Laurentide ice sheet evolution from pluvial paleolake shorelines in the western United States

The deformation pattern of the paleoshorelines of extinct Lake Bonneville were among the first features to indicate that Earth's interior responds viscoelastically to changes in surface loads (Gilbert, 1885). Here we revisit and extend this classic study of isostatic rebound with updated lake chronologies for Lake Bonneville and Lake Lahontan as well as revised elevation datasets of shoreline features. The first order domal pattern in the shoreline elevations can be explained by rebound associated with the removal of the lake load. We employ an iterative scheme to calculate the viscoelastic lake rebound, which accounts for the deformation of the solid Earth and gravity field, to calculate a lake load that is consistent with the load-deformed paleotopography. We find that the domal deformation requires a regional Earth structure that exhibits a thin elastic thickness of the lithosphere (15–25 km) and low sublithospheric Maxwell viscosity (∼1019 Pas). After correcting for rebound due to the lake load, shoreline feature elevations reveal a statistically significant northward dipping trend. We attribute this trend to continent-scale deformation caused by the ice peripheral bulge of the Laurentide ice sheet, and take advantage of the position of these lakes on the distal flank of the peripheral bulge to provide new insights on mantle viscosity and Laurentide ice sheet reconstructions. We perform ice loading calculations to quantify the deformation of the solid Earth, gravity field, and rotation axis that is caused by the growth and demise of the Laurentide ice sheet. We test three different ice reconstructions paired with a suite of viscosity profiles and confirm that the revealed trend can be explained by deformation associated with the Laurentide ice sheet when low viscosities below the asthenosphere are adopted. We obtain best fits to shoreline data using ice models that do not have the majority of ice in the eastern sectors of the Laurentide ice sheet, with the caveat that this result can be affected by lateral variations in viscosity. We show that pluvial lakes in the western United States can place valuable constraints on the Laurentide ice sheet, the shape of its peripheral bulge, and the underlying mantle viscosity.

Microbially influenced lacustrine carbonates: A comparison of Late Quaternary Lahontan tufa and modern thrombolite from Fayetteville Green Lake, NY.

Carbonate microbialites in lakes can serve as valuable indicators of past environments, so long as the biogenicity and depositional setting of the microbialite can be accurately determined. Late Pleistocene to Early Holocene frondose draping tufa deposits from Winnemucca Dry Lake (Nevada, USA), a subbasin of pluvial Lake Lahontan, were examined in outcrop, petrographically, and geochemically to determine whether microbially induced precipitation is a dominant control on deposition. These observations were compared to modern, actively accumulating microbialites from Fayetteville Green Lake (New York, USA) using similar methods. In addition, preserved microbial DNA was extracted from the Lahontan tufa and sequenced to provide a more complete picture of the microbial communities. Tufas are texturally and geochemically similar to modern thrombolitic microbialites from Fayetteville Green Lake, and the stable isotopic composition of organic C, N, inorganic C, and O supports deposition associated with a lacustrine microbial mat environment dominated by photosynthetic processes. DNA extraction and sequencing indicate that photosynthetic microbial builders were present during tufa deposition, primarily Chloroflexi and Proteobacteria with minor abundances of Cyanobacteria and Acidobacteria. Based on the sequencing results, the depositional environment of the tufas can be constrained to the photic zone of the lake, contrasting with some previous interpretations that put tufa formation in deeper waters. Additionally, the presence of a number of mesothermophilic phyla, including Deinococcus-Thermus, indicates that thermal groundwater may have played a role in tufa deposition at sites not previously associated with groundwater influx. The interpretation of frondose tufas as microbially influenced deposits provides new context to interpretations of lake level and past environments in the Lahontan lake basins.

8200‐year growth history of a Lahontan‐age lacustrine tufa deposit

AbstractTufa domes and towers are common around the margins of Winnemucca Dry Lake, Nevada, USA, a desiccated sub‐basin of pluvial Lake Lahontan. A 2·5 m diameter concentrically‐layered tufa mound from the southern end of the playa was sampled along its growth axis to determine timing, rate and geochemical conditions of tufa growth. A radiocarbon‐based age model indicates an 8200‐year tufa depositional record that begins near the end of the Last Glacial Maximum (ca 23 400 cal yr bp) and concludes at the end of the most recent Lahontan highstand (ca 15 200 cal yr bp). Petrography, stable isotopes and major and minor elemental compositions are used to evaluate the rate and timing of tufa growth in the context of the depositional environment. The deposit built radially outward from a central nucleation point, with six decimetre‐scale layers defined by variations in texture. Two distinct tufa types are observed: the inner section is composed of two layers of thinolite pseudomorphs after ikaite, with the innermost layer comprised of very small pseudomorphs (<0·25 cm) and an outer layer composed of larger, ca 3 cm long pseudomorphs, followed by a transitional layer where thinolite pseudomorphs grade into calcite fans. The outer section consists of three distinct layers of thrombolitic micrite with a branching mesofabric. The textural change occurred as lake levels began to rise towards the most recent Lahontan highstand interval and probably was prompted by warming of lake waters caused by increased groundwater flux during highstand lake levels. The Mg/Ca and Sr/Ca variations suggest a warming trend in the tufa growth environment and may also reflect increasing growth rates of tufa associated with increased fluxes of groundwater. This systematic study of tufa deposition indicates the importance of the hydrology of the lacustrine tufa system for reconstructing palaeoenvironmental records, and particularly the interaction of ground and surface waters.

Late Pleistocene to present lake-level fluctuations at Pyramid and Winnemucca lakes, Nevada, USA

AbstractA new lake-level curve for Pyramid and Winnemucca lakes, Nevada, is presented that indicates that after the ~15,500 cal yr BP Lake Lahontan high stand (1338 m), lake level fell to an elevation below 1200 m, before rising to 1230 m at the 12,000 cal yr BP Younger Dryas high stand. Lake level then fell to 1155 m by ~10,500 cal yr BP followed by a rise to 1200 m around 8000 cal yr BP. During the mid-Holocene, levels were relatively low (~1155 m) before rising to moderate levels (1190–1195 m) during the Neopluvial period (~4800–3400 cal yr BP). Lake level again plunged to about 1155 m during the late Holocene dry period (~2800–1900 cal yr BP) before rising to about 1190 m by ~1200 cal yr BP. Levels have since fluctuated within the elevation range of about 1170–1182 m except for the last 100 yr of managed river discharge when they dropped to as low as 1153 m. Late Holocene lake-level changes correspond to volume changes between 25 and 55 km3 and surface area changes between 450 and 900 km2. These lake state changes probably encompass the hydrologic variability possible under current climate boundary conditions.

Glacial chronology of the Sierra Nevada, California, from the Last Glacial Maximum to the Holocene

During the Last Glacial Maximum the Sierra Nevada in California, USA, supported a mountain glacier/ice cap complex that covered over 20,000 km2. The history of this ice cover can be reconstructed using 14C and cosmogenic-nuclide surface-exposure dating. These show that the glaciers reached their maximum extent for the last glacial cycle between 21 and 18 ka, i.e., during the global Last Glacial Maximum. This is termed the Tioga 3 advance. A slow retreat began at 18 ka and accelerated rapidly at about 17 ka. After retreating an unknown distance, the glaciers began to readvance at about 16.7 ka, reaching the Tioga 4 limit at 16.2 ka. They then rapidly retreated to the crest of the range, probably within 500 to 1000 years. There is no indication of subsequent glacial expansion until the Recess Peak advance between 14.0 and 12.5 ka. Unfortunately, chronological control is not adequate to determine whether this advance was during the early Younger Dryas or slightly preceded it. The equilibrium-line-altitude reduction during the Tioga 3 was about 1200 m, that during the Tioga 4 about 800 m, and during the Recess Peak 100 to 200 m. The Tioga 4 advance coincided with the expansion of nearby pluvial Lake Lahontan to its maximum size. The Sierra Nevada advances correlate well with the glacial chronology of the Alps during the same period, and also with the episodes of melting and advance of the European and Laurentide Ice Sheets. Times of glacial advance in the Sierra Nevada may be connected to the melting history of the ice sheets, and to Heinrich events, by expansion and contraction of sea ice in the southern North Atlantic.

Refining fault slip rates using multiple displaced terrace risers—An example from the Honey Lake fault, NE California, USA

Faulted terrace risers are semi-planar features commonly used to constrain Quaternary slip rates along strike-slip faults. These landforms are difficult to date directly and therefore their ages are commonly bracketed by age estimates of the adjacent upper and lower terrace surfaces. However, substantial differences in the ages of the upper and lower terrace surfaces (a factor of 2.4 difference observed globally) produce large uncertainties in the slip-rate estimate. In this investigation, we explore how the full range of displacements and bounding ages from multiple faulted terrace risers can be combined to yield a more accurate fault slip rate. We use 0.25-m cell size digital terrain models derived from airborne lidar data to analyze three sites where terrace risers are offset right-laterally by the Honey Lake fault in NE California, USA. We use ages for locally extensive subhorizontal surfaces to bracket the time of riser formation: an upper surface is the bed of abandoned Lake Lahontan having an age of 15.8 ± 0.6 ka and a lower surface is a fluvial terrace abandoned at 4.7 ± 0.1 ka. We estimate lateral offsets of the risers ranging between 6.6 and 28.3 m (median values), a greater than fourfold difference in values. The amount of offset corresponds to the riser's position relative to modern stream meanders: the smallest offset is in a meander cutbank position, whereas the larger offsets are in straight channel or meander point-bar positions. Taken in isolation, the individual terrace-riser offsets yield slip rates ranging from 0.3 to 7.1 mm/a. However, when the offset values are collectively assessed in a probabilistic framework, we find that a uniform (linear) slip rate of 1.6 mm/a (1.4–1.9 mm/a at 95% confidence) can satisfy the data, within their respective uncertainties. This investigation demonstrates that integrating observations of multiple offset elements (crest, midpoint, and base) from numerous faulted and dated terrace risers at closely spaced sites can refine slip-rate estimates on strike-slip faults.

A paleoseismic transect across the northwestern Basin and Range Province, northwestern Nevada and northeastern California, USA

We use new and existing data to compile a record of ∼18 latest Quaternary large-magnitude surface-rupturing earthquakes on 7 fault zones in the northwestern Basin and Range Province of northwestern Nevada and northeastern California. The most recent earthquake on all faults postdates the ca. 18–15 ka last glacial highstand of pluvial Lake Lahontan and other pluvial lakes in the region. These lacustrine data provide a window in which we calculate latest Quaternary vertical slip rates and compare them with rates of modern deformation in a global positioning system (GPS) transect spanning the region. Average vertical slip rates on these fault zones range from 0.1 to 0.8 mm/yr and total ∼2 mm/yr across a 265-km-wide transect from near Paradise Valley, Nevada, to the Warner Mountains in California. We converted vertical slip rates to horizontal extension rates using fault dips of 30°–60°, and then compared the extension rates to GPS-derived rates of modern (last 7–9 yr) deformation. Our preferred fault dip values (45°–55°) yield estimated long-term extension rates (1.3–1.9 mm/yr) that underestimate our modern rate (2.4 mm/yr) by ∼21%–46%. The most likely sources of this underestimate are geologically unrecognizable deformation from moderate-sized earthquakes and unaccounted-­for coseismic off-fault deformation from large surface-rupturing earthquakes. However, fault dip values of ≤40° yield long-term rates comparable to or greater than modern rates, so an alternative explanation is that fault dips are closer to 40° than our preferred values. We speculate that the large component of right-lateral shear apparent in the GPS signal is partitioned on faults with primary strike-slip displacement, such as the Long Valley fault zone, and as not easily detected oblique slip on favorably oriented normal faults in the region.

Stromatolites in Walker Lake (Nevada, Great Basin, USA) record climate and lake level changes ~ 35,000 years ago

Walker Lake is a closed-basin remnant of the large Pleistocene glacial Lake Lahontan system that has experienced multiple high amplitude (100–200m) changes in water level over the past ~40,000years in response to changes in climate. A laminated carbonate stromatolite composed of varying proportions of calcite fans and micrite was collected from a paleoshoreline located at approximately 58m above present lake level. Radiocarbon dating revealed that the stromatolite spans approximately 2000years of growth, from 35,227 to 33,727 calibrated years before present (YBP), a time period during which paleolake level is not well constrained. Distinct laminae were drilled along the growth axis, and the resulting powders were collected for clumped isotope analyses to generate formation temperatures (lake water temperatures) during stromatolite formation, from which δ18Owater was calculated.Results indicate that the stromatolite experienced an initial increase in temperature and water δ18O values followed by a decrease in both during the course of accretion. The resulting temperature and isotopic data were input into a Rayleigh distillation model for lakewater evaporation in order to estimate the magnitude of lake level and volume fluctuations over the course of accretion. Modeling results reveal a lake level decrease between 8.1 and 15.6m, followed by an increase of between 4.3 and 8.8m during the course of stromatolite growth.The results of this study indicate that Walker Lake experienced significant lake volume change over the course of 2000years, perhaps as a response to precipitation changes driven by fluctuations in the polar jet stream and accompanying changes in regional climate, and/or evaporation-induced changes in lake level. These results add to a growing body of research indicating that stromatolites and other lacustrine tufas represent a detailed and extensive terrestrial archive that can potentially be used to reconstruct the timing and magnitude of climate change.

Application of UAV Photography to Refining the Slip Rate on the Pyramid Lake Fault Zone, Nevada

The Pyramid Lake fault zone (PLFZ) is a 50‐km‐long, active northwest‐trending right‐lateral fault in the northern Walker Lane, located ∼30 km east of Reno, Nevada. Previous paleoearthquake and slip‐rate studies report that the Pyramid Lake fault has produced four surface‐rupturing paleoearthquakes since 15,475±720 cal B.P., three of which occurred after 8980±260 cal B.P., and has had an average minimum slip rate of 2.6±0.3 mm/yr since the late Pleistocene. These observations imply that coseismic offset for each paleoearthquake averaged 7–9 m, larger than expected from empirical scaling relationships for a strike‐slip fault of its length. To reconcile this discrepancy, we used a small camera‐mounted unmanned aerial vehicle to develop high‐resolution digital elevation models and interpret previously unreported right‐laterally offset geomorphic features along the northern section of the PLFZ. Offset measurements at seven sites range from 8 to 21 m. The ages of displaced features are interpreted from previous lake level and mapping studies of Lake Lahontan. From these observations, slip‐rate estimates at the sites range between 0.5 and 1.6 mm/yr. These lower values of slip rate require that coseismic displacements associated with previously reported paleoearthquakes average only 3–5 m, within the range that would be predicted from empirical scaling relationships of rupture length and coseismic displacement.

Conservation genetics of a desert fish species: the Lahontan tui chub (Siphateles bicolor ssp.)

Analysis of the genetic diversity and structure of declining populations is critical as species and populations are increasingly fragmented globally. In the Great Basin Desert in particular, climate change, habitat alteration, and fragmentation threaten aquatic habitats and their endemic species. Tui chubs, including the Lahontan tui chub and Dixie Valley tui chub, (Siphateles bicolor ssp.) are native to the Walker, Carson, Truckee and Humboldt River drainages in the Great Basin Desert. Two populations, Walker Lake and Dixie Valley, are under threat from habitat alteration, increased salinity, small population sizes, and nonnative species. We used nine microsatellite markers to investigate the population genetic structure and diversity of these and nine other tui chub populations to provide information to managers for the conservation of both Walker Lake and Dixie Valley tui chubs. Genetic population structure reflects both historical and contemporary factors, such as connection with Pleistocene Lake Lahontan in addition to more recent habitat fragmentation. Dixie Valley was the most highly differentiated population (pairwise F ST = 0.098−0.217, p < 0.001), showed evidence of a past bottleneck, and had the lowest observed heterozygosity (Ho = 0.607). Walker Lake was not substantially differentiated from other Lahontan tui chub populations, including those located in different watersheds (pairwise F ST = 0.031−0.103, p < 0.001), and had the highest overall observed heterozygosity (Ho = 0.833). We recommend that managers continue to manage and monitor Dixie Valley as a distinct Management Unit, while continuing to maximize habitat size and quality to preserve overall genetic diversity, evolutionary potential, and ecological processes.

The unusual temporal and spatial slip history of the Wassuk Range normal fault, western Nevada (USA): Implications for seismic hazard and Walker Lane deformation

We document temporal and spatial variations in vertical displacement rate across 6 temporal orders of magnitude to better understand how the 100-km-long, east-dipping Wassuk Range normal fault system has accommodated strain in the context of the Walker Lane, a tectonically active, NNW-trending zone of dextral and extensional deformation that affects significant portions of western Nevada and eastern California. We combine 10 Be and 26 Al cosmonuclide exposure ages with shallow seismic and gravity data from the buried hanging wall of the Wassuk fault to derive a post–113 ka (10 5 yr time scale) vertical displacement rate of 0.82 ± 0.16 mm/yr. We also perform large-scale fault scarp analysis to constrain the long-term (>1 Ma; 10 6 yr time scale) displacement rate. Our fault-scarp analysis results imply similar vertical displacement rates, with higher long-term vertical displacement rates along the southern fault (∼1.1 mm/yr) relative to the northern fault ( Vertical displacement rate data at the 10 6 , 10 5 , 10 3 , and 10 1 yr time scales (this study and others) support a constant vertical displacement rate between 0.75 and 1.0 mm/yr for the Wassuk Range fault since ca. 4 Ma. An anomalously high vertical displacement rate at the 10 4 yr time scale is best explained by an earthquake cluster between ca. 15.5 ka and ca. 10.5 ka, potentially linked to rapid filling of the Walker Lake basin immediately prior to the ca. 13 ka Sehoo highstand of ancestral Lake Lahontan. We hypothesize that this flood event induced seismicity by placing an additional load on the hanging wall of the Wassuk Range fault and by increasing the pore-fluid pressure within and adjacent to the fault. Although an earthquake cluster like this is consistent with Wallace-type fault behavior, we suggest that a nontectonic stressor induced the cluster, resulting in the apparent discrepancy in vertical displacement rate at the 10 4 yr time scale. Thus, we posit that the long-term slip along Wassuk fault is better explained by slip-predictable Reid-type behavior, which deviates from the behavior of other well-documented fault systems. Based on these results, we suggest that similar, unrecognized nontectonic stressors may influence rates of strain release along other major fault systems worldwide. Finally, we present a revised model of central Walker Lane kinematics, based on data from this and other recent studies.

Rise and fall of late Pleistocene pluvial lakes in response to reduced evaporation and precipitation: Evidence from Lake Surprise, California

Widespread late Pleistocene lake systems of the Basin and Range Province indicate substantially greater moisture availability during glacial periods relative to modern times, but the climatic factors that drive changes in lake levels are poorly constrained. To better constrain these climatic forcing factors, we present a new lacustrine paleoclimate record and precipitation estimates for Lake Surprise, a closed basin lake in northeastern California. We combine a detailed analysis of lake hydrography and constitutive relationships describing the water balance to determine the influence of precipitation, evaporation, temperature, and seasonal insolation on past lake levels. At its maximum extent, during the last deglaciation, Lake Surprise covered 1366 km 2 (36%) of the terminally draining Surprise Valley watershed. Using paired radiocarbon and 230 Th-U analyses, we dated shoreline tufa deposits from wave-cut lake terraces in Surprise Valley, California, to determine the hydrography of the most recent lake cycle. This new lake hydrograph places the highest lake level 176 m above the present-day playa at 15.19 ± 0.18 calibrated ka ( 14 C age). This significantly postdates the Last Glacial Maximum (LGM), when Lake Surprise stood at only moderate levels, 65–99 m above modern playa, similar to nearby Lake Lahontan. To evaluate the climatic factors associated with lake-level changes, we use an oxygen isotope mass balance model combined with an analysis of predictions from the Paleoclimate Model Intercomparison Project 3 (PMIP3) climate model ensemble. Our isotope mass balance model predicts minimal precipitation increases of only 2%–18% during the LGM relative to modern, compared to an ∼75% increase in precipitation during the 15.19 ka highstand. LGM PMIP3 climate model simulations corroborate these findings, simulating an average precipitation increase of only 6.5% relative to modern, accompanied by a 28% decrease in total evaporation driven by a 7 °C decrease in mean annual temperature. LGM PMIP3 climate model simulations also suggest a seasonal decoupling of runoff and precipitation, with peak runoff shifting to the late spring–early summer from the late winter–early spring. Our coupled analyses suggest that moderate lake levels during the LGM were a result of reduced evaporation driven by reduced summer insolation and temperatures, not by increased precipitation. Reduced evaporation primed Basin and Range lake systems, particularly smaller, isolated basins such as Surprise Valley, to respond rapidly to increased precipitation during late-Heinrich Stadial 1 (HS1). Post-LGM highstands were potentially driven by increased rainfall during HS1 brought by latitudinally extensive and strengthened midlatitude westerly storm tracks, the effects of which are recorded in the region9s lacustrine and glacial records. These results suggest that seasonal insolation and reduced temperatures have been underinvestigated as long-term drivers of moisture availability in the western United States.

Strike-slip faulting along the Wassuk Range of the northern Walker Lane, Nevada

A strike-slip fault is present outboard and subparallel to the Wassuk Range front within the central Walker Lane (Nevada, USA). Recessional shorelines of pluvial Lake Lahontan that reached its highstand ca. 15,475 ± 720 cal. yr B.P. are displaced ∼14 m and yield a right-lateral slip-rate estimate approaching 1 mm/yr. The strike-slip fault trace projects southeastward toward the eastern margin of Walker Lake, which is ∼15 km to the southeast. The trace is obscured in this region by recessional shorelines features that record the historical dessication of the lake caused by upstream water diversion and consumption. High-resolution seismic CHIRP (compressed high intensity radar pulse) profiles acquired in Walker Lake reveal ∼20 k.y. of stratigraphy that is tilted westward ∼20–30 m to the Wassuk Range front, consistent with ∼1.0–1.5 mm/yr (20–30 m/20 k.y.) of vertical displacement on the main range-bounding normal fault. Direct evidence of the northwest-trending right-lateral strike-slip fault is not observed, although a set of folds and faults trending N35°E, conjugate to the trend of the strike-slip fault observed to the north, is superimposed on the west-dipping strata. The pattern and trend of folding and faulting beneath the lake are not simply explained; they may record development of Riedel shears in a zone of northwest-directed strike slip. Regardless of their genesis, the faults and folds appear to have been inactive during the past ∼10.5 k.y. These observations begin to reconcile what was a mismatch between geodetically predicted deformation rates and geological fault slip rate studies along the Wassuk Range front, and provide another example of strain partitioning between predominantly normal and strike-slip faults that occurs in regions of oblique extension such as the Walker Lane.

Dating North America's oldest petroglyphs, Winnemucca Lake subbasin, Nevada

On the west side of the Winnemucca Lake subbasin, Nevada, distinctive deeply carved meter-scale petroglyphs are closely spaced, forming panels on boulder-sized surfaces of a partially collapsed tufa mound. The large, complex motifs at this side are formed by deeply carved lines and cupules. A carbonate crust deposited between 10 200 and 9800 calibrated years B.P. (ka) coats petroglyphs at the base of the mound between elevations of 1202 and 1206 m. Petroglyphs above the carbonate crust are carved into a branching form of carbonate that dates to 14.8 ka. Radiocarbon dates on a multiple-layered algal tufa on the east side of the basin, which formed at an elevation of 1205 m, as well as a sediment-core-based total inorganic carbon record for the period 17.0–9.5 ka indicate that water level in the Winnemucca Lake subbasin was constrained by spill over the Emerson Pass Sill (1207 m) for most of the time between 12.9 ± 0.3 and ≥9.2 ka. These and other data indicate that the lake in the Winnemucca Lake subbasin fell beneath its spill point between 14.8 and 13.2 ka and also between 11.3 and 10.5 ka (or between 11.5 and 11.1 ka), exposing the base of the collapsed tufa mound to petroglyph carving. The tufa-based 14C record supports decreased lake levels between 14.8–13.2 ka and 11.3–10.5 ka. Native American artifacts found in the Lahontan Basin date to the latter time interval. This does not rule out the possibility that petroglyph carving occurred between 14.8 and 13.2 ka when Pyramid Lake was relatively shallow and Winnemucca Lake had desiccated.

Late Quaternary Slip‐Rate Variations along the Warm Springs Valley Fault System, Northern Walker Lane, California–Nevada Border

The extent to which faults exhibit temporally varying slip rates has important consequences for models of fault mechanics and probabilistic seismic hazard. Here, we explore the temporal behavior of the dextral‐slip Warm Springs Valley fault system, which is part of a network of closely spaced (10–20 km) faults in the northern Walker Lane (California–Nevada border). We develop a late Quaternary slip record for the fault using Quaternary mapping and high‐resolution topographic data from airborne Light Distance and Ranging (LiDAR). The faulted Fort Sage alluvial fan (40.06° N, 119.99° W) is dextrally displaced ![Graphic][1] , and we estimate the age of the alluvial fan to be ![Graphic][2] to 55.7±9.2 ka, based on a terrestrial cosmogenic ![Graphic][3] depth profile and ![Graphic][4] analyses on basalt boulders, respectively. The displacement and age constraints for the fan yield a slip rate of ![Graphic][5] to ![Graphic][6] (2 σ ) along the northern Warm Springs Valley fault system for the past 41.4–55.7 ka. In contrast to this longer‐term slip rate, shorelines associated with the Sehoo highstand of Lake Lahontan (∼15.8 ka) adjacent to the Fort Sage fan are dextrally faulted at most 3 m, which limits a maximum post‐15.8 ka slip rate to 0.2 mm/yr. These relations indicate that the post‐Lahontan slip rate on the fault is only about one‐tenth the longer‐term (41–56 ka) average slip rate. This apparent slip‐rate variation may be related to co‐dependent interaction with the nearby Honey Lake fault system, which shows evidence of an accelerated period of mid‐Holocene earthquakes. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif