We examine major reorganizations of the terrestrial ecosystem around Mono Lake, California during the last deglacial period from 16,000–9,000 cal yr BP using pollen, microcharcoal, and coprophilous fungal spores (Sporormiella) from a deep-water sediment core. The pollen results record the assemblage, decline, and replacement of a mixed wooded community of Sierran and Great Basin taxa with Alkali Sink and Sagebrush Steppe biomes around Mono Lake. In particular, the enigmatic presence of Sequoiadendron-type pollen and its extirpation during the early Holocene hint at substantial biogeographic reorganizations on the Sierran-Great Basin ecotone during deglaciation. Rapid regional hydroclimate changes produced structural alterations in pine–juniper woodlands facilitated by increases in wildfires at 14,800 cal yr BP, 13,900 cal yr BP, and 12,800 cal yr BP. The rapid canopy changes altered the availability of herbaceous understory plants, likely putting pressure on megafauna populations, which declined in a stepwise fashion at 15,000 cal yr BP and 12,700 cal yr BP before final extirpation from Mono Basin at 11,500 cal yr BP. However, wooded vegetation communities overall remained resistant to abrupt hydroclimate changes during the late Pleistocene; instead, they gradually declined and were replaced by Alkali Sink communities in the lowlands as temperature increased into the Early Holocene, and Mono Lake regressed.

We use PRISM climatic data (1981–2010) and Landsat images (2012–2013) to establish an empirical relationship linking annual temperature and precipitation to the equilibrium line altitude (ELA) of glaciers in the Sierra Nevada (36–41°N, California, USA). For this, we determined the present-day ELAs of 57 glaciers and the local 0°C isotherms elevation Iso0, averaged over the 1981–2010 period. The difference, for each glacier, is Y, the normalized snowline altitude (Y = ELA – Iso0). We then empirically calibrated a logarithmic relationship between this normalized snowline altitude and mean annual precipitation using data from partially covered glaciers. Our calibration is statistically distinct from that previously established for the tropical and midlatitude Andes (Fox and Bloom [1994], Journal of Geography (Chigaku Zasshi), 103, 867–885; Condom et al. [2007], Global and Planetary Change, 59, 189–202). This new relationship for North America is an easy-to-use tool to permit paleoclimatic reconstructions from paleo-ELAs. For a specific paleoglacial site, paleotemperature can be computed knowing the paleoprecipitation range, and vice versa. We also performed a test showing that, if precipitation is well known, the uncertainty associated with paleotemperature is about 1°C (1σ).

Albitite, locally aegirine- and riebeckite-bearing, formed as a result of sodium metasomatism of felsic dykes and argillites along the Melones Fault Zone near Jamestown, California. Pyrite, magnetite, hematite and titanite are common in small amounts in altered dykes. The dykes were originally plagioclase-hornblende porphyritic, and had major and trace element abundances typical of calc-alkaline rocks, whereas they now have Na2O contents as high as 11.40%. Associated fracture-filling veins are dominated by albite, but locally include aegirine, analcime, paragonite, calcite and sodic scapolite. Quartz is present in most albitic rocks, but is absent in riebeckite- and aegirine-bearing samples. Albitization predated CO2 metasomatism and formation of sericite-pyrite assemblages that are typical of gold deposits of the Mother Lode Belt.

Alkaline fluids responsible for Na-metasomatism had elevated Na+/K+ and Na+/H+ relatively high fO2, and low aH4SiO4. The presence of titanite indicates fluid. The presence of titanite indicates fluid XCO2 was low, in contrast to fluids that formed later carbonate-bearing assemblages. Sodic scapolite suggests that, at least locally, the fluids attained very high salinities.

Mass balance calculations indicate that alteration involved addition of large amounts of sodium, and the removal of SiO2 and K2O. Textural preservation, combined with volume factors calculated from specific gravity and whole rock analytical data, indicate that Na-metasomatism was essentially isovolumetric.

Sodium-rich zones along the Melones Fault Zone are closely associated with fault-bounded bodies of ultramafic rock, typically altered to talc-carbonate or quartz-magnesite-Cr muscovite assemblages. Carbonatization and talc-forming reactions in the ultramafic rocks may lead to SiO2-undersaturated fluids. Expansion of the muscovite stability field in terms of Na+/K+-Na+/H+, as a result of incorporation of Cr (up to 7.7% Cr2O3) in muscovite, would result in H+- and K+-depletion as the fluid interacts with ultramafic rocks. This could lead to fluids with elevated Na+/K+ and high pH, as documented in this occurrence.

Reconstruction of lake-level fluctuations from landform and outcrop evidence typically involves characterizing periods with relative high stands. We developed a new approach to provide water-level estimates in the absence of shoreline evidence for Owens Lake in eastern California by integrating landform, outcrop, and existing lake-core data with wind-wave and sediment entrainment modeling of lake-core sedimentology. We also refined the late Holocene lake-level history of Owens Lake by dating four previously undated shoreline features above the water level (1096.4 m) in AD 1872. The new ages coincide with wetter and cooler climate during the Neopluvial (~3.6 ka), Medieval Pluvial (~0.8 ka), and Little Ice Age (~0.35 ka). Dates from stumps below 1096 m also indicate two periods of low stands at ~0.89 and 0.67 ka during the Medieval Climatic Anomaly. The timing of modeled water levels associated with 22 mud and sand units in lake cores agree well with shoreline records of Owens Lake and nearby Mono Lake, as well as with proxy evidence for relatively wet and dry periods from tree-ring and glacial records within the watershed. Our integrated analysis provides a continuous 4000-yr lake-level record showing the timing, duration, and magnitude of hydroclimate variability along the south-central Sierra Nevada.

Lichenometry accurately dates exposure times of glacial moraines and landslides when measuring the longest axis of the largest crustose lichen on many blocks, as demonstrated by numerous examples. In Sweden, the sizes of Rhizocarpon subgenus Rhizocarpon describe five pulses of glacial moraine creation in 120 yr. Six historic California earthquakes, between AD 1800 and 1906, caused many landslides that constrain lichen growth as linear with a dating accuracy of±0.5 yr. Crustose lichen sizes date earthquake-created additions to Sierra Nevada talus with an accuracy of±5 yr. The oldest lichen ages are 400 yr for Lecanora sierrae, 800 yr for Lecidea atrobrunnea, and 1100 yr for Acarospora chlorophana and Rhizocarpon subgenus Rhizocarpon. Lichen sizes also record differing spatial attenuation of ground shaking from the magnitude (Mw) ~7.9 San Andreas earthquake of AD 1857 and the more distant, smaller San Jacinto AD 1800 earthquake, which both caused Sierra Nevada rockfalls. AD 1800 seismic shaking was relatively stronger than that of AD 1857 farther north, perhaps expressing stronger Love and Rayleigh styles of surface waves from the north-trending AD 1800 surface rupture that were particularly efficient in causing rockfalls at greater distances.

An experiment was established in 1961 to determine the influence of bearmat (Chamaebatia foliolosa Benth.) competition on ponderosa pine (Pinus ponderosa Laws.) survival and growth. Ponderosa pine seedlings were planted in bearmat which was: (A) untreated, (B) sprayed with a mixture of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and (C) eliminated by a combination of herbicide, clipping sprouts, and trenching to prevent root and rhizome invasion. Ponderosa pine survival after 19 yr averaged 9%, 66%, and 90%, respectively, for the three treatments. Tree height after 19 yr averaged 1.6, 1.9, and 5.7 m for treatments A, B, and C, respectively. Soil moisture use was initially less on the herbicide-treated than on the untreated plots, but bearmat quickly sprouted after application to compete with the pine seedlings for moisture. After 19 yr the bearmat was more dense and appeared to be more vigorous on the sprayed plots than on those receiving no treatment. We estimate that 75% reduction in net wood production could result after 50 yr on this site from bearmat competition.

Chironomid remains from a mid-elevation lake in the Sierra Nevada, California, were used to estimate quantitative summer surface water temperatures during the past ∼15,000 yr. Reconstructed temperatures increased by ∼3°C between lake initiation and the onset of the Holocene at ∼10,600 cal yr BP (calibrated years before present). Temperatures peaked at 6500 cal yr BP, displayed high variability from 6500 to 3500 cal yr BP, and stabilized after 3500 cal yr BP. This record generally tracks reconstructed Santa Barbara Basin sea surface temperatures (SSTs) through much of the Holocene, highlighting the correspondence between SST variability and California land temperatures during this interval.

Sediment records from two lakes in the east-central Sierra Nevada, California, provide evidence of cooling and hydrological shifts during the Younger Dryas stade (YD; ~ 12,900–11,500 cal yr BP). A chironomid transfer function suggests that lake-water temperatures were depressed by 2°C to 4°C relative to maximum temperatures during the preceding Bølling–Allerød interstade (BA; ~ 14,500–12,900 cal yr BP). Diatom and stable isotope records suggest dry conditions during the latter part of the BA interstade and development of relatively moist conditions during the initiation of the YD stade, with a reversion to drier conditions later in the YD. These paleohydrological inferences correlate with similar timed changes detected in the adjacent Great Basin. Vegetation response during the YD stade includes the development of more open and xeric vegetation toward the end of the YD. The new records support linkages between the North Atlantic, the North Pacific, and widespread YD cooling in western North America, but they also suggest complex hydrological influences. Shifting hydrological conditions and relatively muted vegetation changes may explain the previous lack of evidence for the YD stade in the Sierra Nevada and the discordance in some paleohydrological and glacial records of the YD stade from the western United States.

Detailed pollen, charcoal, isotope and magnetic susceptibility data from an alpine lake sediment core from Sierra Nevada, southern Spain record changes in vegetation, fire history and lake sedimentation since ca. 4100 cal yr BP. The proxies studied record an arid period from ca. 3800 to 3100 cal yr BP characterized by more xerophytic vegetation and lower lake levels. A humid period is recorded between ca. 3100 and 1850 cal yr BP, which occurred in two steps: (1) an increase in evergreen Quercus between 3100 and 2500 cal yr BP, indicating milder conditions than previously and (2) an increase in deciduous Quercus and higher lake levels, between ca. 2500 and 1850 cal yr BP, indicating a further increase in humidity and reduction in seasonal contrast. Humid maxima occurred during the Roman Humid Period, previously identified in other studies in the Mediterranean region. Intensified fire activity at this time could be related to an increase in fuel load and/or in human disturbance. An arid period subsequently occurred between 1850 and 650 cal yr BP, though a decrease in Quercus and an increase in xerophytes. The alternation of persistent North Atlantic Oscillation modes probably played an important role in controlling these humid–arid cycles.

Here, we present two high-resolution records of macroscopic charcoal from high-elevation lake sites in the Sierra Nevada, California, and evaluate the synchroneity of fire response for east- and west-side subalpine forests during the past 9200 yr. Charcoal influx was low between 11,200 and 8000 cal yr BP when vegetation consisted of sparse Pinus-dominated forest and montane chaparral shrubs. High charcoal influx after 8000 cal yr BP marks the arrival of Tsuga mertensiana and Abies magnifica, and a higher-than-present treeline that persisted into the mid-Holocene. Coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the Sierra Nevada after 3800 cal yr BP. Independent fire response occurs between 9200 and 5000 cal yr BP, and significant synchrony at 100- to 1000-yr timescales emerges between 5000 cal yr BP and the present, especially during the last 2500 yr. Indistinguishable fire-return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late Holocene. Fires after 1200 cal yr BP are often synchronous and corroborate with inferred droughts. Holocene fire activity in the high Sierra Nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the El Niño–Southern Oscillation.

The chemistry of the carbonate-free clay-size fraction of Owens Lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial–interstadial oscillations. Owens Lake records of total organic carbon, magnetic susceptibility, and chemical composition of the carbonate-free, clay-size fraction indicate that Tioga glaciation began ∼24,500 and ended by ∼13,60014C yr B.P. Many of the components of glacial rock flour (e.g., TiO2, MnO, BaO) found in Owens Lake sediments achieved maximum values during the Tioga glaciation when valley glaciers reached their greatest extent. Total organic carbon and SiO2(amorphous) concentrations reached minimum values during Tioga glaciation, resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of Owens Lake. At least 20 stadial–interstadial oscillations occurred in the Sierra Nevada between 52,600 and 14,00014C yr B.P. Total organic carbon data from a Pyramid Lake sediment core also indicate oscillations in glacier activity between >39,500 and ∼13,60014C yr B.P. Alpine glacier oscillations occurred on a frequency of ≤1900 yr in both basins, suggesting that millennial-scale oscillations occurred in California and Nevada during most of the past 52,600 yr.

Mono Lake sediments have recorded five major oscillations in the hydrologic balance between A.D. 1700 and 1941. These oscillations can be correlated with tree-ring-based oscillations in Sierra Nevada snowpack. Comparison of a tree-ring-based reconstruction of the Pacific Decadal Oscillation (PDO) index (D’Arrigo et al., 2001) with a coral-based reconstruction of Subtropical South Pacific sea-surface temperature (Linsley et al., 2000) indicates a high degree of correlation between the two records during the past 300 yr. This suggests that the PDO has been a pan-Pacific phenomena for at least the past few hundred years. Major oscillations in the hydrologic balance of the Sierra Nevada correspond to changes in the sign of the PDO with extreme droughts occurring during PDO maxima. Four droughts centered on A.D. 1710, 1770, 1850, and 1930 indicate PDO-related drought reoccurrence intervals ranging from 60 to 80 yr.

n-Alkane biomarker distributions in sediments from Swamp Lake (SL), in the central Sierra Nevada of California (USA), provide evidence for an increase in mean lake level ~ 3000 yr ago, in conjunction with widespread climatic change inferred from marine and continental records in the eastern North Pacific region. Length distributions of n-alkane chains in modern plants growing at SL were determined and compared to sedimentary distributions in a core spanning the last 13 ka. As a group, submerged and floating aquatic plants contained high proportions of short chain lengths (< nC25) compared to emergent, riparian and upland terrestrial species, for which chain lengths > nC27 were dominant. Changes in the sedimentary n-alkane distribution over time were driven by variable inputs from plant sources in response to changing lake level, sedimentation and plant community composition. A shift toward shorter chain lengths (nC21,nC23) occurred between 3.1 and 2.9 ka and is best explained by an increase in the abundance of aquatic plants and the availability of shallow-water habitat in response to rising lake level. The late Holocene expansion of SL following a dry mid-Holocene is consistent with previous evidence for increased effective moisture and the onset of wetter conditions in the Sierra Nevada between 4.0 and 3.0 ka.

Chemical analyses of the clay-sized fractions of 564 continuous sediment samples (200-yr resolution) from composite core OL90/92 allow quantification of an abundance of glacial rock flour. Rock flour produced during glacier advances is represented by clay-sized plagioclase, K-feldspar, and biotite in homogeneous internal composition. The abundance of rock flour is deemed proportional to the intensity of glacies advances. Age control for the composite section is provided by combining previously published radiocarbon dates on organics, U/Th dates on ostracode shells, and U/Th dates on saline minerals from nearby Searles Lake correlated to OL92 by pollen. The rock flour record displays three levels of variability: (1) a dominant one of about 20,000 yr related to summer insolation and precipitation; (2) an intermediate one of 3000–5000 yr, perhaps related to North Atlantic Heinrich events; and (3) a minor one of 1000–2000 yr, perhaps related to North Atlantic thermohaline-driven air-temperature variation.

One of the highest priority invasive species at both Yosemite and Sequoia and Kings Canyon national parks is Holcus lanatus L. (common velvetgrass), a perennial bunchgrass that invades mid-elevation montane meadows. Despite velvetgrass being a high priority species, there is little information available on control techniques. The goal of this project was to evaluate the short-term response of a single application of common chemical and manual velvetgrass control techniques. The study was conducted at three montane sites in Yosemite National Park. Glyphosate spot-spray treatments were applied at 0.5, 1.0, 1.5, and 2.0% concentrations, and compared with hand pulling to evaluate effects on cover of common velvetgrass, cover of other plant species, and community species richness. Posttreatment year 1 cover of common velvetgrass was 12.1% ± 1.6 in control plots, 6.3% ± 1.5 averaged over the four chemical treatments (all chemical treatments performed similarly), and 13.6% ± 1.7 for handpulled plots. This represents an approximately 50% reduction in common velvetgrass cover in chemically- treated plots recoded posttreatment year 1 and no statistically significant reduction in hand pulled plots compared with controls. However, there was no treatment effect in posttreatment year 2, and all herbicide application rates performed similarly. In addition, there were no significant treatment effects on nontarget species or species richness. These results suggest that for this level of infestation and habitat type, (1) one year of hand pulling is not an effective control method and (2) glyphosate provides some level of control in the short-term without impact to nontarget plant species, but the effect is temporary as a single year of glyphosate treatment is ineffective over a two-year period.

Downy brome (Bromus tectorum) is an invasive, annual grass that has spread through much of the Great Basin desert but remains patchy at high elevation. This study evaluates control options for outlier infestations in the eastern Sierra Nevada, CA, based on their ecological effectiveness and their economic and practical feasibility. I tested the efficacy of hand-pulling, sheet-mulching, and soil solarization followed by broadcast and seedball seeding of native forbs and grasses. Downy brome cover, density, and dominance in the seed bank decreased with all removal treatments. Soil solarization and sheet mulching were most successful at eliminating downy brome (decreasing density by 99% after just 1 yr of treatment in both cases), but they had negative nontarget impacts on other herbaceous species. Germination of native seeds was low with both broadcast and seedball seeding, probably because of dry conditions. Each of the methods tested has potential for decreasing or eliminating small-scale, outlier infestations of downy brome along roadsides and in disturbed sites and thereby helping to contain the invasion.

Dansgaard–Oeschger (D–O) cycles had far-reaching effects on Northern Hemisphere and tropical climate systems during the last glacial period, yet the climatic response to D–O cycles in western North America is controversial, especially prior to 55 ka. We document changes in precipitation along the western slope of the central Sierra Nevada during early Marine Oxygen Isotope Stages (MIS) 3 and 4 (55–67 ka) from a U-series dated speleothem record from McLean's Cave. The timing of our multi-proxy geochemical dataset is coeval with D–O interstadials (15–18) and stadials, including Heinrich Event 6. The McLean's Cave stalagmite indicates warmer and drier conditions during Greenland interstadials (GISs 15–18), signified by elevated δ18O, δ13C, reflectance, and trace element concentrations, and less radiogenic 87Sr/86Sr. Our record extends evidence of a strong linkage between high-latitude warming and reduced precipitation in western North America to early MIS 3 and MIS 4. This record shows that the linkage persists in diverse global climate states, and documents the nature of the climatic response in central California to Heinrich Event 6.

Development of an accurate chronology for glacial deposits in the Sierra Nevada has long been problematic given the lack of suitable organic material for radiocarbon dating. Lichenometry initially appeared promising as ages showed an increase from cirque headwalls to down-canyon moraines. However, while Recess Peak lichen age estimates range from 2 to 3 ka, recent work shows these deposits to be at least 10 ka older. Here, we present evidence for a late Holocene reset of Recess Peak lichen ages by significant post-depositional climate change. Following late-Pleistocene deposition of Recess Peak moraines, warming through the mid-Holocene allowed forests to advance into shallow basins eliminating local inverted tree lines. This produced a partial canopy where shading killed the original post-Pleistocene crustose lichen colonies. Late-Holocene cooling resulted in forest retreat from these basins as alpine tree line fell. Lichens then recolonized the re-exposed Recess Peak deposits. We conclude that while Recess Peak lichen ages are accurate to within the dating uncertainty of the technique, existing lichen ages actually date the timing of post-mid-Holocene cooling and recolonization, and not the original emplacement of these deposits. Thus, applications of Lichenometry should consider post-depositional environmental change when interpreting the meaning of these dates.

The Miocene–Quaternary Trans-Mexican Volcanic arc is thought to have grown southwards (i.e. trenchward) since the Pliocene. This theory is mainly supported by roughly N–S-directed polygenetic volcanic ranges along which volcanic activity migrates southwards with time. We investigated the eruptive history of one of these ranges, the Sierra Nevada (east boundary of Mexico City basin), by compiling literature ages and providing new K–Ar dates. Our K–Ar ages are the first ones for the northernmost Tláloc and Telapón volcanoes and for the ancestral Popocatépetl (Nexpayantla). The obtained ages reveal that the four stratovolcanoes forming the range worked contemporaneously during most of the Middle to Late Pleistocene. However, taking into account the onset of the volcanic activity, a southward migration is evidenced along the Sierra Nevada: volcanism initiated at its northern tip at least 1.8 Ma ago at Tláloc volcano, extended southwards 1 Ma ago with Iztaccíhuatl and appeared at its southern end 329 ka ago with the Nexpayantla cone. Such a migration would be most probably primarily driven by Cocos slab roll-back and steepening rather than by regional crustal tectonics, which played a secondary role by controlling the apparent alignment of the volcanoes.

Pupae and pupal exuviae were collected by drift and hand netting from 27 sites on 10 streams in the Sierra Nevadamountains in 1986 and 1987. The sites represented an altitudinal range from 340 m to 2100 m. The pupal exuviae collections revealed a composite fauna of 143 species. Eukiefferiella (12 spp.) and Tvetenia (3 spp.) were dominant both taxonomically and numerically along most of the altitudinal profile, followed by Cricotopus (11 spp.), Orthocladius (9 spp.) and Diamesa (7 spp.). The altitudinal distribution of the 99 most common species is shown and compared with those obtained in other Europeanstreams or rivers, especially in the Pyrenees. The general pattern of altitudinal zonation shows an increase in speciesrichness from the headwaters (< 2000 m : 58 spp.) toward the middle reaches (1000-1600 m : 121 spp.). The theoreticallyexpected highest species richness in the foothill reaches (> 1000 m : 113 spp.) was not obtained. The periods of reduced or intermittent flow, the domestic organic inputs and the narrowness of the channels in the foothill reaches appear responsible for the decrease of the species richness of the chironomid communities.