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The Transverse Ranges of southern California often experience fire followed by flood. This sequence sometimes causes post-fire debris flows (PFDFs) that threaten life and property situated on alluvial fans. The combination of steep topography, highly erodible rock and soil, and wildfire, coupled with intense rainfall, can initiate PFDFs even in cases of relatively small storm rainfall totals. This study identifies common atmospheric conditions during which damaging PFDFs occur in the Transverse Ranges during the cool season, defined here as November-March. A compilation of 93 PFDF events during 1980-2014 triggered by 19 precipitation events is compared against previous studies of the events, reanalysis, precipitation, and radar data to estimate PFDF trigger times. Each event was analyzed to determine common atmospheric features and their range of values present at and preceding the trigger time. Results show atmospheric rivers are a dominant feature, observed in 13 of the 19 events. Other common features include low-level winds orthogonal to the Transverse Ranges and other conditions favorable for orographic forcing, a strong upper level jet south of the region, and moist-neutral static stability. Several events included closed low-pressure systems or narrow cold frontal rain bands. These findings can help forecasters identify more precisely the synoptic-scale atmospheric conditions required to produce PFDF-triggering rainfall and thus reduce uncertainty when issuing warnings. [ABSTRACT FROM AUTHOR]

The Ventura Avenue anticline is one of the fastest uplifting structures in southern California, rising at ~5 mm/yr. We use well data and seismic reflection profiles to show that the anticline is underlain by the Ventura fault, which extends to seismogenic depth. Fault offset increases with depth, implying that the Ventura Avenue anticline is a fault-propagation fold. A decrease in the uplift rate since ~30 ± 10 ka is consistent with the Ventura fault breaking through to the surface at that time and implies that the fault has a recent dip-slip rate of ~4.4-6.9 mm/yr. To the west, the Ventura fault and fold trend continues offshore as the Pitas Point fault and its associated hanging wall anticline. The Ventura-Pitas Point fault appears to flatten at about 7.5 km depth to a detachment, called the Sisar decollement, then step down on a blind thrust fault to the north. Other regional faults, including the San Cayetano and Red Mountain faults, link with this system at depth. We suggest that below 7.5 km, these faults may form a nearly continuous surface, posing the threat of large, multisegment earthquakes. Holocene marine terraces on the Ventura Avenue anticline suggest that it grows in discrete events with 5-10 m of uplift, with the latest event having occurred ~800 years ago (Rockwell, 2011). Uplift this large would require large earthquakes (Mw 7.7-8.1) involving the entire Ventura/Pitas Point system and possibly more structures along strike, such as the San Cayetano fault. Because of the local geography and geology, such events would be associated with significant ground shaking amplification and regional tsunamis. [ABSTRACT FROM AUTHOR]

The widely held perception that the San Andreas fault (SAF) is vertical or steeply dipping in most places in southern California may not be correct. From studies of potential-field data, active-source imaging, and seismicity, the dip of the SAF is significantly nonvertical in many locations. The direction of dip appears to change in a systematic way through the Transverse Ranges: moderately southwest (55°-75°) in the western bend of the SAF in the Transverse Ranges (Big Bend); vertical to steep in the Mojave Desert; and moderately northeast (37°-65°) in a region extending from San Bernardino to the Salton Sea, spanning the eastern bend of the SAF in the Transverse Ranges. The shape of the modeled SAF is crudely that of a propeller. If confirmed by further studies, the geometry of the modeled SAF would have important implications for tectonics and strong ground motions from SAF earthquakes. The SAF can be traced or projected through the crust to the north side of a well documented high-velocity body (HVB) in the upper mantle beneath the Transverse Ranges. The north side of this HVB may be an extension of the plate boundary into the mantle, and the HVB would appear to be part of the Pacific plate. [ABSTRACT FROM AUTHOR]

Understanding the relationship between mating trait evolution and speciation requires data from a variety of taxa. I analysed the calling songs of the shield-back katydid genus Aglaothorax, which represents a little-known lineage of acoustic insects. Field-collected males of all described species and most subspecies were recorded under controlled laboratory conditions. Discriminant analysis was 90.5% successful in separating song types, but the song types thus delineated did not correspond to currently recognized taxa as defined by morphology. The discrepancy is caused by two species, Aglaothorax morsei and Aglaothorax longipennis, the songs of which vary in a cline across the Transverse Ranges and the Los Angeles Basin of southern California. From west to east, pulse rate and duty cycle decrease and interpulse interval increases. Selection for species recognition at a contact zone, sexual selection and interactions between signals and the environment are considered as causes of the cline. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, , 910-921. [ABSTRACT FROM AUTHOR]

Aim The Mohave ground squirrel ( Xerospermophilus mohavensis) is one of a few endemic species of the Mojave Desert of south-western North America. We describe phylogeographic patterns within this species and its sister taxon ( Xerospermophilus tereticaudus) and test hypotheses concerning their biogeographical history using genetic signatures of stable versus expanding populations. We compare these patterns with those of other Mojave species to evaluate the role of vicariance in producing phylogeographic structure during the assembly of the Mojave Desert biota. Location The Mojave Desert and adjacent desert regions of south-western North America. Methods Complete cytochrome b gene sequences of X. mohavensis (46 individuals representing 11 localities) and X. tereticaudus (38 individuals representing 14 localities) were analysed using Bayesian methods to infer phylogenetic relationships. Genetic signals of stable or expanding populations were examined based on the distribution of recent mutations and pairwise differences, as well as with a coalescent-based approach. Results The two species are reciprocally monophyletic and may have diverged in response to the late Pliocene–early Pleistocene uplift of the Transverse Ranges and Mojave block. Little phylogeographic structure is evident within X. mohavensis, but there is a signature of northern expansion from a presumably full-pluvial refugium in the Mojave River basin. Four geographic subgroups are evident within X. tereticaudus, and there is a signature of northern expansion from a presumably full-pluvial refugium in the Sonoran coastal plains. Roughly congruent phylogeographic patterns are found within five arid-adapted taxa, indicating a strong element of vicariance during the assembly of the generally transitional Mojave Desert biota. Main conclusions We present a preliminary model for the historical assembly of the Mojave Desert biota that indicates a strong vicariant element producing autochthonous lineages (including X. mohavensis) that diverged during the major geological and climatic events of the last 5 Myr. Phylogeographic partitioning within the Mojave Desert underscores the necessity of immediate conservation measures for this unique and fragile arid ecosystem that is locked between two large metropolitan population centres and is the target of continued adverse environmental impact. [ABSTRACT FROM AUTHOR]

Background: Comparative phylogeography of sympatric sibling species provides an opportunity to isolate the effects of geography and demographics on the evolutionary history of two lineages over the same, known time scale. In the current study, we investigated the phylogeographic structure of two zopherid beetle species, Phloeodes diabolicus and P. plicatus, where their ranges overlap in California's Transverse Ranges. Results: Although P. diabolicus and P. plicatus share similar habitats with largely overlapping distributions, the results of this study revealed different evolutionary histories for each species since divergence from their most recent common ancestor. In general, P. plicatus had higher genetic diversity, and more among population isolation than P. diabolicus. The mismatch distributions indicated that one major difference between the two species was the timing of population expansion. This result was consistent with genetic patterns revealed by the Фst values and genetic diversity. Lastly, there were no parallel genetic breaks at similar geographic barriers between the species. Conclusions: Our data revealed that differential demographics rather than geography were responsible for the genetic patterns of the two species. [ABSTRACT FROM AUTHOR]

Sediment yields from the world's rivers are generally highest from steep drainage basins with weak lithology, active tectonics, or severe land-use impacts. Here, we evaluate sediment yields from the Western Transverse Ranges of California in an attempt to explain why they are two- to tenfold greater than the surrounding areas of California. We found that suspended-sediment yields across the gauged basins of the Western Transverse Range during 1969-1999 varied by approximately an order of magnitude (740-5300 t/ km2/yr). Similarly, fine-sediment concentrations for normalized discharge rates varied by almost two orders of magnitude (e.g., 1.3-110 g/L for the mean annual flood) for 11 previously unmonitored drainages of the Santa Ynez Mountains. Areas with high sediment yields consistently have weakly consolidated bedrock (Quaternary-Pliocene marine formations) and are associated with the highest rates of tectonic uplift of the region (>5 mm/ yr). These regions are important to the sediment discharge budgets, because ~50 % of the total suspended-sediment discharge from the Western Transverse Range is estimated to be generated within these regions, even though they represent only ~10% of the total watershed area. Previous estimates of suspended-sediment discharge from the Ventura River have likely been underestimated by ~50% because the gauging station is located immediately upstream of a high sediment yield region. We also found a significant and positive correlation between sediment yield and the percentage of a watershed with grassland and agricultural land use. These results suggest that there is adequate variation within the lithology, tectonics, and land use of the broader Western Transverse Range geologic province to induce large variations in sediment yield at the local scale. [ABSTRACT FROM AUTHOR]

Trophic linkages between terrestrial and aquatic ecosystems are increasingly recognized as important yet poorly known features of food webs. Here we describe research to understand the dynamics of lake food webs in relation to a native riparian amphibian and its interaction with introduced trout. The mountain yellow-legged frog Rana muscosa is endemic to alpine watersheds of the Sierra Nevada Mountains and the Transverse Ranges of California, but it has declined to a small fraction of its historical distribution and abundance. Although remaining frogs and introduced trout feed in different habitats of alpine lakes, our stable-isotope analyses clearly show that the same resource base of benthic invertebrates sustains their growth. During one period, insect emergence from naturally fishless lakes was nearly 20-fold higher compared to adjacent lakes with trout, showing that fish reduce availability of aquatic prey to amphibious and terrestrial consumers. Although trout cannot prey on adult frogs due to gape limitation, foraging post-metamorphic frogs are 10 times more abundant in the absence of trout, suggesting an important role for competition for prey by trout in highly unproductive alpine watersheds. Most Sierran lakes contain fish, and those that do not are usually small isolated ponds; in our study, these two lake types supported the lowest densities of post-metamorphic frogs, and these frogs were less reliant on local, benthic sources of productivity. Since Rana muscosa was formerly the most abundant vertebrate in the Sierra Nevada, the reduction in energy flow from lake benthos to this consumer due to fish introductions may have had negative consequences for its numerous terrestrial predators, many of which have also declined. We suggest that disruptions of trophic connections between aquatic and terrestrial food webs are an important but poorly understood consequence of fish introduction to many thousands of montane lakes and streams worldwide and may contribute to declines of native consumers in riparian habitats. [ABSTRACT FROM AUTHOR]

Abstract: Transpressional tectonics are typically associated with restraining bends on major active strike-slip faults, resulting in uplift and steep terrain. This produces dynamic erosional and depositional conditions and difficulties for established lines of palaeoseismological investigation. Consequently, in these areas data are lacking to determine tectonic behaviour and future hazard potential along these important fault segments. The Big Bend of the San Andreas fault in the Transverse Ranges of southern California exemplifies these problems. However, landslides, probably seismically triggered, are widespread in the rugged terrain of the Big Bend. Fluvial reworking of these deposits rapidly produces geomorphic planes and lines that are markers for subsequent fault slip. The most useful are offset and abandoned stream channels, for these are relatively high precision markers for identifying individual faulting events. Palaeoseismological studies from the central Big Bend, involving 14C ages of charcoal fragments from trench exposures, illustrate these points and indicate that the past three faulting events, including the great 1857 earthquake, were relatively similar in scale, each producing offsets of about 7–7.5 m. The mean recurrence interval is 140–220 years. The pre-1857 event here may be the 1812 event documented south of the Big Bend or an event which took place probably between 1630 and 1690. Ground breakage in both events extended south of the Big Bend, unlike the 1857 event where rupture was skewed to the north. The preceding faulting event ruptured both to the north and south of the Big Bend and probably occurred between 1465 and 1495. All these events centred on the Big Bend and may be typical for this fault segment, suggesting that models of uniform long-term slip rates may not be applicable to the south-central San Andreas. A slip-rate estimate of 34–51 mm a−1 for the central Big Bend, although uncertain, may also imply higher slip in the Big Bend and highlights difficulties in correlating slip-rates between sites with different tectonic settings. Slip rates on the San Andreas may increase within the broad compressional tectonics zone of the Big Bend, compared to the north and south where the plate boundary is a relatively linear and sub-parallel series of dominantly strike-slip faults. Partitioning slip within the Big Bend is inherently uncertain and insufficient suitably comparable data are available to sustain a uniform slip model, although such models are a common working assumption. [Copyright &y& Elsevier]

A 2-D upper crustal structural profile with seven steeply dipping faults was constructed from the Los Angeles Region Seismic Experiment phase II (LARSE II) seismic refraction data recorded over the north central Transverse ranges and adjacent Mojave desert in southern California. The profile extends to a depth of approximately 4 km. The faults were identified from distinctive features in the seismic first arrival data, while the velocity structure was determined from travel times and refined by forward modelling. The resulting seismic velocity structure is correlative to the geological structure along the profile and is used to help constrain a geological cross-section. Six of the seven faults detected from the seismic data correspond directly to geologically mapped faults in the central Transverse ranges and adjacent Mojave desert. From south to north, they are the Pelona fault, the San Francisquito fault, the Clearwater fault, the San Andreas fault and two faults that cut the Portal ridge. The seventh fault is buried beneath Quaternary deposits of the western Mojave desert and appears to correlate with an additional fault that cuts Portal ridge out of the section line. The southernmost fault (the Pelona fault) separates the younger Vasquez formation in the south from the Pelona schist in the north and is determined to be an intermediate (40°–60°) south-dipping normal fault. This coupled with field observations indicate that the Pelona fault was instrumental in the late Oligocene—early Miocene formation of the Soledad basin, and the structural ascent and exhumation of the Pelona schist along the proto-Sierra Pelona intrabasin ridge. Analogous Neogene extensional deformation is found to have affected the western Mojave desert region, where faults 6 and 7 appear to have had north side down normal displacement and to have been instrumental in forming the western Antelope basin. A 6.0 km s−1 basal layer to our shallow seismic structure is correlated with the Pelona schist south of the San Andreas fault and with the tectonically related Rand schist beneath the western Mojave desert. Granitic and gneissic crystalline rocks, which form regional upper plate complexes along the Vincent thrust above the Pelona schist and along the Rand thrust above the Rand schist, yield consistently low seismic velocities as compared with the expected velocities for the constituent rock types. These anomalous velocities are reconciled by the degraded structural and textural state of the upper plate crystalline rocks that resulted from extreme shearing, brittle fracturing and related retrogressive hydration reactions starting during or shortly after the latest Cretaceous—early Palaeocene underthrusting of the schists. Extension, translation along the San Andreas transform system and compressional faulting with the uplift of the Transverse ranges further accentuated the basement deformations. The integrated result is that the survival of the Precambrian through Mesozoic granitic crust of the region became a rootless and highly attenuated upper crustal layer. [ABSTRACT FROM AUTHOR]

Proposes a listric thrust model for the western Transverse Ranges in California. Fault-related folds; Fold-and-thrust belts; Listric faults; Santa Barbara Channel; Santa Maria basin; Santa Monica Mountains.

Apatite fission-track (FT) and (U–Th)/He analyses are used to constrain the low-temperature thermal history of the San Gabriel and San Bernardino Mountains (SGM and SBM), which are part of the southern California Transverse Ranges. FT ages from 33 SGM samples range from 3 to 64 Ma. Helium ages, ranging from 3 to 43 Ma, were obtained from 13 of these samples: all of the He ages are the same or younger than their respective FT ages. FT ages from 10 SBM samples were older, ranging from 45 to 90 Ma. The FT and He data document at least three phases of cooling in the SGM, but only two in the SBM. Prior to ~7 Ma, the thermal history of the SGM appears to have been nearly identical to many of the core complexes in the Basin and Range of south-eastern California: a major phase of cooling is indicated from ~60 to 40 Ma, with a more recent phase beginning at ~23 Ma and continuing until ~10 Ma. The similarity of this timing to that of core complexes suggests that the SGM also originated as a core complex, when the rocks were adjacent to the Chocolate–Orocopia Mountains, and that some of the range-bounding faults were initially extensional. In the SBM, the two phases of cooling documented by the FT data occurred from ~65 to 55 Ma, and from ~18 Ma to the present. The timing on the second phase is very poorly constrained and, therefore, we do not speculate on the origin of the SBM. The most recent phase of cooling appears to have begun at ~7 Ma in the SGM, as the result of the onset of contractional deformation. A more accelerated phase of cooling may have begun at ~3 Ma. Distinct variations in the total amounts and rates of cooling between different fault-bounded blocks within the SGM are documented since 7 Ma. We use these variations in cooling rates to calculate denudation rates, which are then compared to topographic characteristics for each structural block. These comparisons suggest that more rapid bedrock uplift in the eastern and southern part of the... [ABSTRACT FROM AUTHOR]

Assesses the influence of a variety of environmental variables on among-site variation in riparian vegetation of southern California Transverse Ranges. Effects of elevation, unit stream power, fire history and valley on the composition of vegetation; Species groups generated by TWINSPAN classification.

Presents deterministic maps of P-wave scatterers in the upper mantle beneath Southern California over 5600 short-period recordings of teleseismic events. Kirchhoff coda migration (KCM) method; Schematic illustration of the wave field from a point scatterer at depth; Application of KCM to 13 years of teleseismic seismicity recorded by the Southern California Seismograph Network.