Geologic Model for Alluvium-Buttressed Landslides

Temporal and spatial patterns in the architecture of the Franciscan Complex provide valuable insights into the subduction processes through which such patterns arise. The Nacimiento Franciscan belt is an allochthonous sliver of subduction assemblages in the central California Coast Ranges displaced either: (1) from southern California by >300 km of Neogene dextral slip along the San Andreas fault system or (2) from central California to southern California and back again, by >500 km of Late Cretaceous–Paleocene sinistral slip along the Sur-Nacimiento fault followed by San Andreas–related motion. New U-Pb detrital zircon data from 20 (meta)clastic samples indicate that the Nacimiento Franciscan section was assembled between ca. 95 and 80 Ma. Abundant Cretaceous (particularly Late Cretaceous) and diminishing amounts of Jurassic and Proterozoic zircon grains point to a southern California origin for Nacimiento Franciscan protoliths, precluding significant sinistral strike-slip along the Sur-Nacimiento fault. Furthermore, the suite of detrital zircon ages reported here bears a strong resemblance to new and existing data from subduction complexes in southern California that were emplaced during Laramide shallow subduction (i.e., Sierra de Salinas, Portal Ridge, Quartz Hill, Rand, San Emigdio, and Tehachapi schists). Hence, the Nacimiento Franciscan is distinct from Franciscan rocks in central and northern California and more likely represents an outboard element of the Late Cretaceous southern California low-angle subduction system. Upon restoring the Nacimiento block to its Late Cretaceous position, an inboard-younging trend is apparent in the composite Nacimiento–southern California schist belt, suggesting that progressively younger accretionary materials were underplated farther inboard by tectonic erosion. We posit that arc and forearc elements absent from southern California were removed by a combination of physical and tectonic erosion attending shallow subduction, interleaved in the subduction complex, and recycled into the mantle. Steepening of the Laramide slab was marked by a phase of crustal extension in the overriding plate. During this phase, the Sur-Nacimiento fault likely functioned as a segment of a low-angle normal fault system spanning the southern Sierra Nevada batholith to the Nacimiento accretionary system.

Aim The salamander Ensatina eschscholtzii Gray is a classic example of a ring species, or a species that has expanded around a central barrier to form a secondary contact characterized by species‐level divergence. In the original formulation of the ring species scenario, an explicit biogeographical model was proposed to account for the occurrence of intraspecific sympatry between two subspecies in southern California (the ‘southern closure’ model). Here we develop an alternative ring species model that is informed by the geomorphological development of the California Coast Ranges, and which situates the point of ring closure in the Monterey Bay region of central coastal California (the ‘Monterey closure’ model). Our study has two aims. The first is to use phylogenetic methods to evaluate the two competing biogeographical models. The second is to describe patterns of phylogeographical diversity throughout the range of the Ensatina complex, and to compare these patterns with previously published molecular systematic data.Location Western North America, with a focus on the state of California, USA.Methods We obtained mitochondrial DNA sequence data from 385 individuals from 224 populations. A phylogeny was inferred using Bayesian techniques, and the geographical distributions of haplotypes and clades were mapped. The two biogeographical ring species models were tested against our Bayesian topology, including the associated Bayesian 95% credible set of trees.Results High levels of phylogeographical diversity were revealed, especially in central coastal and northern California. Our Bayesian topology contradicts the Monterey closure model; however, 0.08% of the trees in our Bayesian 95% credible set are consistent with this model. In contrast, the classic ring species biogeographical model (the southern closure model) is consistent with our Bayesian topology, as were 99.92% of the trees in our 95% credible set.Main conclusions Our Bayesian phylogenetic analysis most strongly supports the classic ring species model, modified to accommodate an improved understanding of the complex geomorphological evolution of the California Coast Ranges. In addition, high levels of phylogeographical diversity in central and northern California were identified, which is consistent with the striking levels of allozymic differentiation reported previously from those regions.

Large pressure gap between the Coastal and Central Franciscan belts, northern and central California

In the California Current System, poleward flow has been observed at different levels and in different seasons. In winter, there is broad poleward flow at the surface along most of the coast along Washington, Oregon, and northern California. During the upwelling season, in spring and summer, there is a narrow, inshore poleward surface current which appears off northern California whenever upwelling-favorable winds weaken; off southern and central California, this inshore poleward flow seems to persist through most of the upwelling season. During the upwelling season, there is also subsurface poleward flow, both near the bottom over much of the continental shelf and at depths of a few hundred meters along the upper continental slope. Whether and how these “branches” of poleward flow are related to each other is still unknown. We have some ideas of how the surface poleward flows are driven, but still very little information on the continuity and the driving of the subsurface undercurrents. In this note, we shall summarize briefly the main characteristics of each of these “branches,” and present some recent observations of the California Undercurrent in the CODE region near San Francisco.

Inorganic geochemical indicators of glacial-interglacial changes in productivity and anoxia on the California continental margin

A comparison of the deep structure along nine recent transects of the west margin of North America shows many important similarities and differences. Common tectonic elements identified in the deep structure along these transects include actively subducting oceanic crust, accreted oceanic/arc (or oceanic-like) lithosphere of Mesozoic through Cenozoic ages, Cenozoic accretionary prisms, Mesozoic accretionary prisms, backstops to the Mesozoic prisms, and undivided lower crust. Not all of these elements are present along all transects. In this study, nine transects, including four crossing subduction zones and five crossing transform faults, are plotted at the same scale and vertical exaggeration (V.E. 1 : 1), using the above scheme for identifying tectonic elements. The four subduction-zone transects contain actively subducting oceanic crust, Cenozoic accretionary prisms, and bodies of basaltic rocks accreted in the Cenozoic, including remnants of a large, oceanic plateau in the Oregon and Vancouver Island transects. Rocks of age and composition (Eocene basalt) similar to the oceanic plateau are currently subducting in southern Alaska, where they are doubled up on top of Pacific oceanic crust and have apparently created a giant asperity, or impediment to subduction. Most of the subduction-zone transects also contain Mesozoic accretionary prisms, and two of them, Vancouver Island and Alaska, also contain thick, tectonically underplated bodies of late Mesozoic/early Cenozoic oceanic lithosphere, interpreted as fragments of the extinct Kula plate. In the upper crust, most of the five transform-fault transects (all in California) reflect: (1) tectonic wedging of a Mesozoic accretionary prism into a backstop, which includes Mesozoic/early Cenozoic forearc rocks and Mesozoic ophiolitic/arc basement rocks; and (2) shuffling of the subduction margin of California by strike-slip faulting. In the lower crust, they may reflect migration of the Mendocino triple junction northward (seen in rocks east of the San Andreas fault) and cessation of Farallon-plate subduction (seen in rocks west of the San Andreas fault). In northern California, lower-crustal rocks east of the San Andreas fault have oceanic-crustal velocity and thickness and contain patches of high reflectivity. They may represent basaltic rocks magmatically underplated in the wake of the migration of the Mendocino triple junction, or they may represent stalled, subducted fragments of the Farallon/Gorda plate. The latter alternative does not fit the accepted ‘slabless window’ model for the migration of the triple junction. This lower-crustal layer and the Moho are offset at the San Andreas and Maacama faults. In central California, a similar lower-crustal layer is observed west of the San Andreas fault. West of the continental slope, it is Pacific oceanic crust, but beneath the continent it may represent either Pacific oceanic crust, stalled, subducted fragments (microplates) of the Farallon plate, or basaltic rocks magmatically underplated during subduction of the Pacific/Farallon ridge or during breakup of the subducted Farallon plate. The transect in southern California is only partly representative of regional structure, as the structure here is 3-dimensional. In the upper crust, a Mesozoic prism has been thrust beneath crystalline basement rocks of the San Gabriel Mountains and Mojave Desert. In the mid-crust, a bright reflective zone is interpreted as a possible ‘master’ decollement that can be traced from the fold-and-thrust belt of the Los Angeles basin northward to at least the San Andreas fault. A Moho depression beneath the San Gabriel Mountains is consistent with downwelling of lithospheric mantle beneath the Transverse Ranges that appears to be driving the compression across the Transverse Ranges and Los Angeles basin.

Previous studies have indicated a large model disagreement in the future projections of precipitation changes over the regions featuring Mediterranean climate. Many of these highly populated regions have been experiencing major droughts in the recent decades, raising concerns about future precipitation changes and their impacts. Here we investigate precipitation projections across five Mediterranean climate regions in the CMIP6 ensemble, and study their respective model agreements on the sign of future precipitation changes. We focus on the period 2050-2079 relative to 1970-1999, and consider two climate change scenarios (ssp2-4.5 and ssp5-8.5) over the Mediterranean Basin (MED), California (CAL), the central coast of Chile (SAA), the Cape Province area of South Africa (SAF) and southwest Australia (AUS).The CMIP6 ensemble mean suggests that annual mean cumulative precipitation will decrease over all the regions studied with the exception of northern California. In most cases, this decline is primarily attributed to a reduction in winter precipitation, except over the Mediterranean Basin, where the most significant decrease occurs in autumn. The model agreement on the sign of future precipitation changes is generally high over the regions and seasons where the ensemble mean indicates the precipitation decline in the future, and low over the regions showing the precipitation increase or no change. Specifically, the model agreement is low in southern California during all seasons, in northern Mediterranean during winter and autumn, and in southwest Australia during austral summer and autumn. CMIP6 ensemble means also indicate that the consecutive dry days (CDD) will increase in the future in all regions, but again the model agreement on this increase is low over southern and central California, the southern Mediterranean, and parts of southwest Australia. Similarly, the ensemble mean of consecutive wet days (CWD) indicate a decrease in all regions, with weak model agreement on the sign of future changes over CAL, northeast AUS and part of the MED region. The ensemble mean maximum one-day precipitation increases over all the regions, the most over the parts of southwest Australia and the Mediterranean.We conclude that despite substantial improvements to the new CMIP6 generation of models, the intermodel differences in future projections of precipitation changes continue to be high across parts of California, the Mediterranean Basin and southwest Australia. Impact studies need to account for these uncertainties and consider the whole intermodel range of projected precipitation changes.

The conservation status of the northern California black walnut (Juglans hindsii (Jeps.) Jeps. ex R. E. Sm.) has been a source of considerable confusion and controversy. Although not currently legally protected by either Federal or State Endangered Species Acts, this species is given conservation status by the California Native Plant Society and the California Department of Fish and Wildlife, and some California counties require mitigation for removal of individuals of this species, especially older trees. Despite the current widespread distribution in northern California and southern Oregon of trees that match J. hindsii morphologically, there are only three or four sites where the species is known to have occurred prior to extensive settlement of California by Europeans in the mid-19th century. This has led to the suspicion that trees found in other places may not be genetically pure J. hindsii but may instead be descendants of lineages that experienced past gene flow from one or more other species. In addition, despite its more distant relationship, the cultivated walnut (J. regia L.) readily hybridizes (as the male parent) with J. hindsii, producing morphologically identifiable ‘Paradox' hybrids, which occur spontaneously and are widely planted as rootstocks and street trees. Finally, recent collections of J. hindsii from southern California have raised questions about the respective geographic distributions of J. hindsii and southern California black walnut (J. californica S. Watson). We analyzed genotypes at 10 microsatellite loci for 158 mostly wild J. hindsii trees, as well as some orchard waifs, from 10 counties in northern and southern California and one county in southern Oregon, including representatives of putative original native populations. We also sampled several Paradox hybrids, 10-20 standards for each of the five North American black walnut species, and six standards for J. regia. Bayesian cluster analyses with the program STRUCTURE revealed that at least 71.5% of the putatively wild J. hindsii represent genetically pure members of that species, while the remaining trees show evidence of past hybridizations with one or more of the other North American black walnut species. We found no evidence of introgression of J. regia into J. hindsii. The results suggest that individual J. hindsii trees should not have conservation status.

She retired as library services manager in August 2012, after twentyfive years of

Counts of pinnipeds provide a minimal estimate of population size because some unknown proportion of individuals is in the water during surveys. We determined a correction factor (CF) for Pacific harbor seals (Phoca vitulina richardii) by estimating the proportion ashore of 180 seals tagged with flipper‐mounted radio tags throughout California. The mean proportions of tagged individuals ashore during four complete surveys in 2004 were not different between central and northern California (F= 1.85, P= 0.18) or between sexes (F= 0.57, P= 0.45), but a lesser proportion of weaners was ashore than subadults or adults (F= 7.97, P= 0.001), especially in northern California. The CF calculated for the statewide census of harbor seals was 1.65, using transmitters operating during the survey (n= 114). Using a mark‐recapture estimator for tag survival (phi) and the four telemetry surveys the mean CF for central and northern California was 1.54 ± 0.38 (95% CI). A CF for southern California of 2.86 was based on a single survey. Using the mean CF of 1.54 and a statewide count in 2009 we estimated 30,196 (95% CI = 22,745–37,647) harbor seals in California.

Tectonic deformation as manifested by seismicity and active faulting in the Coast Ranges in the vicinity of Lake Berryessa appears to be concentrated along the Green Valley-Cedar Roughs fault trend and to a lesser degree, the Coast Ranges-Sierran block (CRSB) boundary zone. The Green Valley-Cedar Roughs fault trend appears to be a complex, discontinuous or segmented shear zone consisting of multiple faults. Geomorphic evidence of Quaternary displacement exists along many portions of the fault trend with Holocene features and evidence for fault creep occurring along the Green Valley fault. In contrast, no historic earthquakes greater than ML 5 are known to have occurred along the fault trend. Earthquakes relocated in this study from 1970 to 1988 occur in the vicinity of mapped faults; however, the seismicity is discontinuous with a strong tendency to occur in clusters. Also superimposed on the general north-northwest fault trend are north-south epicentral trends not associated with any mapped faults. Focal mechanisms suggest predominantly right-lateral, strike-slip faulting on both north and north-northwest-trending planes. The existence of reverse and normal focal mechanisms also attests to the complex faulting occurring along the Green Valley-Cedar Roughs trend. In general, the geologic and seismogenic characteristics are consistent with the hypothesis that the Green Valley-Cedar Roughs fault trend represents young faulting, possibly related to a newly developing plate boundary east of the San Andreas fault. Earthquakes are confined to the top 12 km of the upper crust. Seismicity within the CRSB boundary zone since 1970 has been generally confined to a sequence in 1978 near Madison with a mainshock of ML 4.2. Thrust/reverse faulting appears to be the source of this activity, consistent with the seismogenic processes observed along other segments of the boundary zone. Only one earthquake has occurred since 1970 in the epicentral area of the 1892 ML 6¾ Vacaville-Winters earthquake. The state of stress in the Lake Berryessa region as exhibited by focal mechanisms appears to be characterized by NE-directed tectonic compression as observed elsewhere away from the San Andreas fault system in northern and central California.

THE HISTORY of power transmission in northern and central California and the interconnection of hydroelectric and steam-electric plants dates back to just before the turn of the century. Development of water power was given impetus by the earlier uses of water in mining operations. The availability of petroleum fuels encouraged construction of steam plants in areas lacking in hydro power, or where it was needed for purposes of assuring the power supply in low water periods, or in case of interruption of long transmission circuits.

The objectives of this paper are (1) to determine the degree to which the disposal of oil spill wastes in the northern half of California is a problem, (2) to make specific recommendations as to how the disposal situation might be improved, and (3) to put forth general theories as to why the problem exists. The paper, following an information section for those unfamiliar with northern California, is organized so that each objective is examined in turn. Thus, the first section describes the system being analyzed; the second, third, and fourth sections are entitled, respectively, “The Disposal Situation,” “Recommendations,” and “Why Is There a Problem?” The paper finds there is a very serious potential problem in the disposal of oil spills wastes outside the immediate San Francisco Bay area. Specific recommendations for improvement are made and hypothesis as to why the problem exists are given.

At small spatial and temporal scales, genetic differentiation is largely controlled by constraints on gene flow, while genetic diversity across a species' distribution is shaped on longer temporal and spatial scales. We assess the hypothesis that oceanographic transport and other seascape features explain different scales of genetic structure of giant kelp, Macrocystis pyrifera. We followed a hierarchical approach to perform a microsatellite-based analysis of genetic differentiation in Macrocystis across its distribution in the northeast Pacific. We used seascape genetic approaches to identify large-scale biogeographic population clusters and investigate whether they could be explained by oceanographic transport and other environmental drivers. We then modelled population genetic differentiation within clusters as a function of oceanographic transport and other environmental factors. Five geographic clusters were identified: Alaska/Canada, central California, continental Santa Barbara, California Channel Islands and mainland southern California/Baja California peninsula. The strongest break occurred between central and southern California, with mainland Santa Barbara sites forming a transition zone between the two. Breaks between clusters corresponded approximately to previously identified biogeographic breaks, but were not solely explained by oceanographic transport. An isolation-by-environment (IBE) pattern was observed where the northern and southern Channel Islands clustered together, but not with closer mainland sites, despite the greater distance between them. The strongest environmental association with this IBE pattern was observed with light extinction coefficient, which extends suitable habitat to deeper areas. Within clusters, we found support for previous results showing that oceanographic connectivity plays an important role in the population genetic structure of Macrocystis in the Northern hemisphere.

Molecular genetic analysis has long been used to identify species or populations that otherwise may be difficult to distinguish. More than 100 species of rockfish (genus Sebastes) occur worldwide, and more than 50 species may be found in relatively small regions, such as the Monterey Bay or Channel Islands in central and southern California. Many species are morphologically similar, particularly during the early larval stages, and identification to the species level is time‐consuming and problematic for some groups. We describe a simple genetic method for the rapid identification of rockfish species by means of multilocus nuclear genotypes from a panel of six microsatellite loci. Application to a set of known rockfish tissue samples, including fish collected in different parts of their geographic ranges and species not represented in the reference data set, resulted in high assignment accuracy for the represented species and exclusion of the nonrepresented species. Members of the subgenus Pteropodus, for which assignment is difficult with the standard six‐locus panel, are accurately identified to the species level with an additional five loci selected for that purpose. Together, these panels correctly assigned 97.4% of the tested individuals from a group of more than 30 species commonly found in central California.