Point Arena Research Articles

Surface circulation downstream of the Point Arena upwelling center

Measurements from recently installed 5 MHz high-frequency radar (CODAR) stations south of Point Arena, California, are used to describe surface current patterns during the upwelling season (June–August 2007). The systems provide hourly current maps on a 5-km grid, covering a region from approximately 10 to 150 km offshore (the continental shelf into the deep ocean). These HF-radar observations provide an unprecedented view of circulation in this “coastal transition zone”, between the wind-driven circulation over the shelf and the California Current circulation offshore. Circulation patterns include: (1) bifurcation of the coastal upwelling jet downstream of Point Arena into an along-shelf (down-coast) branch and an offshore branch, and (2) a large-scale anticyclonic meander that often develops into an eddy-like recirculation south of the bifurcation. The “recirculation” feature extends well offshore, with surface currents 50–100 km from the coast consistently opposing the wind stress. The spatial and temporal evolution of the surface current features during upwelling events affects surface transport from Point Arena to areas in the south, increasing the travel time of a substantial fraction of newly upwelled water from a few days to roughly two weeks. Thus, surface currents even far offshore influence coastal transport of nutrients, phytoplankton and larvae on ecologically relevant timescales, with resultant connectivity patterns very different than implied by a simple examination of the mean flow.

Mesoscale structure and oceanographic determinants of krill hotspots in the California Current: Implications for trophic transfer and conservation

Krill (crustaceans of the family Euphausiacea) comprise an important prey field for vast array of fish, birds, and marine mammals in the California Current and other large marine ecosystems globally. In this study, we test the hypothesis that mesoscale spatial organization of krill is related to oceanographic conditions associated with coastal upwelling. To test this, we compiled a climatology of krill distributions based on hydroacoustic surveys off California in May–June each year between 2000 and 2009 (missing 2007). Approximately 53,000 km of ocean habitat was sampled, resulting in a comprehensive geo-spatial data set from the Southern California Bight to Cape Mendocino. We determined the location and characteristics of eight definite and two probable krill “hotspots” of abundance. Directional-dependence analysis revealed that krill hotspots were oriented in a northwest–southeast (135°) direction, corresponding to the anisotropy of the 200–2000 m isobath. Krill hotspots were disassociated (inversely correlated) with three upwelling centers, Point Arena, Point Sur, and Point Conception, suggesting that krill may avoid locations of strong offshore transport or aggregate downstream from these locations. While current fisheries management considers the entire coast out to the 2000 m isobath critical habitat for krill in this ecosystem, we establish here smaller scale structuring of this critical mid-trophic level prey resource. Identifying mesoscale krill hotspots and their oceanographic determinants is significant as these smaller ecosystem divisions may warrant protection to ensure key ecosystem functions (i.e., trophic transfer) and resilience. Furthermore, delineating and quantifying krill hotspots may be important for conservation of krill-predators in this system.

Dispersion and connectivity estimates along the U.S. west coast from a realistic numerical model

Near-surface particle dispersion, larval dispersal and connectivity along the U.S west coast were explored using a realistic numerical model of the California Current System. Seasonal model velocities were qualitatively and quantitatively evaluated using Global Drifter Program data. The model displayed a clear seasonal cycle of eddy energy near the coast with energy maxima southwest of major headlands. Eddy speeds were correlated with drifter-based estimates during summer and fall when compared spatially. Over six million passive, Lagrangian particles were released in the upper 20 m of the water column within 10 km of the California and Oregon coasts and tracked for 7 years. The effect of subgridscale vertical turbulence was parameterized with a random walk model. Resulting trajectories yielded climatological maps of particle dispersion. Particle densities varied with release region, release season and time-since-release. Dispersal distances and coastal connectivity varied with season of release, release location, release depth and pelagic larval duration (PLD). Connectivity was clearly influenced by major geographic features such as the Gulf of the Farallones and Cape Mendocino. Given a moderate (30-60 day) PLD, mean dispersal distances varied from ~10-230 km, with standard deviations of ~130-220 km. For release locations from Palos Verdes to Point Sur, the primary direction of dispersal was northward for a moderate PLD, regardless of season. For long PLDs (120-180 day), mean dispersal distances were larger (~40-440 km), with standard deviations of ~330540 km. In winter given a long PLD, dispersal was primarily southward for release locations north of Point Arena. Increasing release depths to 40-60 m altered mean dispersal distances by 50-250 km polewards, but had little effect on standard deviations. Point Conception did not act as a barrier to dispersal for source regions in the Southern California Bight.

Incorporation of Spatial and Economic Analyses of Human-Use Data in the Design of Marine Protected Areas

Social, economic, and ecological criteria contribute to the successful design, implementation, and management of marine protected areas (MPAs). In the context of California's Marine Life Protection Act Initiative, we developed a set of methods for collecting, compiling, and analyzing data about the spatial extent and relative economic importance of commercial and recreational fishing. We interviewed 174 commercial fishers who represented the major fisheries in the initiative's north-central coast region, which extends from Point Arena south to Pigeon Point. These fishers provided data that we used to map the extent of each of the fishing grounds, to weight the relative importance of areas within the grounds, to characterize the operating costs of each fishery, and to analyze the potential economic losses associated with proposed marine protected areas. A regional stakeholder group used the maps and impact analyses in conjunction with other data sets to iteratively identify economic and ecological trade-offs in designations of different areas as MPAs at regional, port, and fishery extents. Their final proposed MPA network designated 20% of state waters as MPAs. Potential net economic loss ranged from 1.7% to 14.2% in the first round of network design and totaled 6.3% in the final round of design. This process is a case study in the application of spatial analysis to validate and integrate local stakeholder knowledge in marine planning.

Overall Status and Threats Assessment of Black Abalone (Haliotis CracherodiiLeach, 1814) Populations in California

The black abalone (Haliotis cracherodii Leach, 1814) is a relatively large prosobranch gastropod mollusc ranging from approximately Point Arena in northern California to Bahia Tortugas and Isla Guadalupe, Mexico. In the United States, populations of black abalone on offshore islands, especially those of southern California, were particularly large prior to the mid 1980s. Analysis of long-term fishery-dependent and -independent data revealed that fishing pressure in combination with a lethal disease, withering syndrome, has resulted in mass mortalities of 95% or greater in black abalone populations south of Monterey County, CA. Reduction in local densities below the threshold necessary for successful fertilization (0.34/m2) has been a widespread and pervasive consequence of population reductions by withering syndrome and other factors. The most significant current and future threat that the black abalone faces is that imposed by the spread of withering syndrome, known to be enhanced by periods of ocean warming. Other factors, such as illegal take, ocean pollution, and natural predation, also pose risks to remaining populations and those that may be restored via active management in the future. Without identification, development, and implementation of effective measures to counter the population-level effects of withering syndrome, remaining black abalone populations may experience further declines.

Some Ectoparasites and Pathogens of the Point Arena Mountain Beaver (Aplodontia rufa nigra)

The Point Arena Mountain Beaver (Aplodontia rufa nigra) is 1 of 7 subspecies of mountain beaver, and occurs as an entirely disjunct population in a 62 km2 area of southcentral coastal Mendocino County, CA (USFWS 1998). Although the Point Arena Mountain Beaver was listed as ' 'endangered' ' in 1991 under the federal Endangered Species Act (USFWS 1998), there are few published scientific papers regarding the biology of this subspecies, and none regarding its parasites or pathogens. We surveyed the ectoparasite fauna of the Point Arena Mountain Beaver and estimated the prevalence of ectoparasite infestation (the proportion of individuals in the host population that are parasitized by each taxon) to provide information on disease or other threats that might affect the subspecies. Approximately 30 ectoparasitic species, including mites (Acari), ticks (Ixodida), fleas (Siphonaptera), and a beetle (Coleoptera) have been documented on other subspecies of mountain beavers (Ferris 1918; Cooley and Kohls 1945; Whitaker and others 1979; Canaris and Bowers 1992). Some of these ectoparasites are host-specific, likely as a result of the unique phylogeny and ecology of the mountain beaver (Feldhamer and others 2003). Given the highly host-specific nature of the mountain beaver ectoparasite community, and the conservation status of the Point Arena subspecies, we also sought to document the presence of any hostspecific ectoparasitic arthropods potentially at risk (Stork and Lyal 1993; Lewis and Lewis 1994). We also tested some of the ectoparasites collected and tissues from salvaged Point Arena Mountain Beavers for evidence of selected

Habitat Characteristics at Den Sites of the Point Arena Mountain Beaver (Aplodontia rufa nigra)

The Point Arena mountain beaver (Aplodontia rufa nigra) is a federally listed endangered species, but has been the subject of few studies. Mountain beavers use burrows that include a single subterranean den. Foremost among the information needs for this subspecies is a description of the above-ground habitat features associated with dens. Using telemetry we located dens of 23 individuals in Manchester State Park, Mendocino County, California. We measured vegetation and topographic variables directly above the dens and at two available sites within the same burrow system. Alternative resource selection functions, based on multivariate expressions of important ecological characteristics, were developed to model features associated with dens. The best model contained three variables: MEANDENS (mean vegetation density), PAMBTOP4 (cover of the four plant species most frequently used), and COSASPECT (cosine aspect). Interestingly, PAMBTOP4 was negatively associated with dens, indicating that dens were not chosen for their proximity to important plant species. Topography plays an important role in that western and northern aspects were favored and SLOPE was included in the second-highest ranked model. Cross validation indicated moderate stability for the top model suggesting that potentially important predictors that were excluded from the analysis (e.g., soil characteristics, social context) may be influential. Nonetheless, we demonstrated that dense vegetation and aspect/slope considerations are more important predictors of Point Arena mountain beaver den selection than proximity to cover of important plant species. Our results apply to Point Arena mountain beaver populations in coastal shrub communities; den selection may be different farther inland, in forests.

Dynamics of wind‐driven upwelling and relaxation between Monterey Bay and Point Arena: Local‐, regional‐, and gyre‐scale controls

In north and central California, equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season. When the winds temporarily weaken, the upwelling flows between Point Reyes and Point Arena “relax,” becoming strongly poleward over the shelf. Analytical and numerical models are used to describe the effect of alongshore variability of winds, bathymetry, and basin‐scale pressure gradients on the strength of upwelling and its relaxation. Alongshore winds weaken to the south of Point Reyes, and the shelf becomes narrower from Point Reyes to Monterey Bay. Both of these lead to reduced upwelling at and to the north of Point Reyes, causing an alongshore gradient of temperature and density on the shelf. These alongshore gradients lead to an along‐isobath pressure gradient over the shelf that drive the relaxation flows. A simple analytical model is used to explain the dynamics, magnitude, and structure of the relaxation flows. The modeling also suggests that the depth of origin of the upwelled waters, and thus their temperature, is controlled by the along‐isobath pressure gradient that exists over the continental slope. This along‐slope pressure gradient is also responsible for the California undercurrent in this region. This pressure gradient is not generated in a model of the Californian coast extending from 32°N to 42°N and integrated for several months, suggesting it is caused by dynamics whose spatial or temporal scales are larger than the Californian coast and/or longer than several months.

Spatial variability of recruitment in the sand crab Emerita analoga throughout California in relation to wind-driven currents

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 350:1-17 (2007) - DOI: https://doi.org/10.3354/meps07208 Spatial variability of recruitment in the sand crab Emerita analoga throughout California in relation to wind-driven currents Jennifer M. Diehl1, Robert J. Toonen2,*, Louis W. Botsford1 1Department of Wildlife, Fish and Conservation Biology, University of California, Davis, California 95616, USA 2School of Ocean and Earth Science and Technology, The Hawai’i Institute of Marine Biology, University of Hawai’i at Manoa, Coconut Island, PO Box 1346, Kane’ohe, Hawai’i 96744, USA *Corresponding author. Email: toonen@hawaii.edu ABSTRACT: We compared recruitment of the sand crab Emerita analoga over 2 yr at 17 sites distributed along >800 km of the California coastline. We hypothesized that larvae of benthic invertebrates are retained by water circulation near headlands, and then redistributed alongshore north of the promontories during synoptic-scale relaxation in upwelling winds. We tested for a negative relationship between recruitment and distance north of 4 headlands: Point Arena, Point Reyes, Monterey Peninsula, and Point Conception. We also examined patterns of recruitment at sites east of Point Conception, within the Southern California Bight (SCB). Recruitment magnitude was predictable at a given site within a recruitment season (June through October), but not between the 2 years at each site. Recruitment of E. analoga north of Point Conception was negatively correlated with site distance north of a headland in 1998, but not in 1999. Upwelling indices in 1998 were not significantly different from the long-term average either north of Point Conception or within the SCB; in contrast, during 1999, upwelling was stronger than the 54 yr average at all sites north of Point Conception, but not at those within the SCB. Thus, the upwelling-relaxation mechanism appeared to operate effectively from Point Arena to Point Conception in 1998, when upwelling and wind stress were within long-term average levels, but not in 1999, when upwelling and wind stress were anomalously high. However, in the SCB, we observed similar magnitude and spatial patterns of recruitment in both years. One implication of our results is that the California coast may be composed of separate retentive cells of populations separated by headlands, which enhances population persistence, but the extent of larval loss from these cells remains unknown. KEY WORDS: Upwelling · Relaxation · Wind stress · Inner shelf · Larval transport · Settlement Full text in pdf format NextCite this article as: Diehl JM, Toonen RJ, Botsford LW (2007) Spatial variability of recruitment in the sand crab Emerita analoga throughout California in relation to wind-driven currents. Mar Ecol Prog Ser 350:1-17. https://doi.org/10.3354/meps07208Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 350. Online publication date: November 22, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Phytoplankton scales of variability in the California Current System: 2. Latitudinal variability

The California Current System encompasses a southward flowing current which is perturbed by ubiquitous mesoscale variability. The extent to which latitudinal patterns of physical variability are reflected in the distribution of biological parameters is poorly known. To investigate the latitudinal distribution of chlorophyll variance, a wavelet analysis is applied to nearly 9 years (October 1997 to July 2006) of 1‐km‐resolution Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) chlorophyll concentration data at 5‐day resolution. Peaks in the latitudinal distribution of chlorophyll variance coincide with features of the coastal topography. Maxima in variance are located offshore of Vancouver Island and downstream of Heceta Bank, Cape Blanco, Point Arena, and possibly Point Conception. An analysis of dominant wavelengths in the chlorophyll data reveals a transfer of energy into smaller scales is generated in the vicinity of the coastal capes. The latitudinal distribution of variance in sea level anomaly corresponds closely to the chlorophyll variance in the nearshore region (<100 km offshore), suggesting that the same processes determine the distribution of both. Farther offshore, there is no correspondence between latitudinal patterns of sea level anomaly and chlorophyll variance. This likely represents a transition from physical to biological control of the phytoplankton distribution.

Nearshore retention of upwelled waters north and south of Point Reyes (northern California)—Patterns of surface temperature and chlorophyll observed in CoOP WEST

Abstract Retentive embayments can be found near capes in upwelling regions, where they stand out as relatively warm features with higher chlorophyll a concentrations than surrounding waters. Within the area of the “Wind Events and Shelf Transport” study site (WEST) from the Gulf of the Farallones to Point Arena (37.5–39°N and 122.5–124°W), we describe two retentive embayments, extending approximately 20 km north of Point Reyes, and 30 km south of Point Reyes in the northern Gulf of the Farallones. These areas are identifiable from chlorophyll a (SeaWiFS) and sea-surface temperature (MODIS) satellite radiometry. Additional data from moorings and drifters were used to further characterize these retentive features. The persistence of these features is on time scales between 2 and 10 days, determined from time-series analysis of mooring data for chlorophyll and temperature. The alongshore wind stress is negatively correlated with chlorophyll and temperature mooring values. The time scale of persistence of these retentive features was similar to both the upwelling-relaxation timescale and the timescale of phytoplankton bloom development. The WEST region is notable in that the spring and summer is subject to the strongest wind stress along the US west coast, yet the coastal waters are highly productive. Based on our observations, we suggest that the apparent persistence of high biomass coastal waters in this strongly advective and wind-dominated system may be partially explained by the presence of retentive features identified in this study.

Development and characterization of microsatellite markers in the Point Arena mountain beaver Aplodontia rufa nigra

AbstractThe Point Arena mountain beaver (Aplodontia rufa nigra) is an endangered subspecies. Efforts to recover this sub‐species will be aided by advances in molecular genetics, specifically the ability to estimate population size using noninvasive genetic sampling. Here we report on the development of nine polymorphic loci for the Point Arena mountain beaver. These markers provide us sufficient power to distinguish individuals, and thus can be used for calculating population size and delineating population substructure.

Asymmetry in elastic properties and the evolution of large continental strike‐slip faults

We use geodetic studies to quantify several cases of significant asymmetry in interseismic and coseismic effects along large continental strike‐slip faults using simple two‐dimensional edge dislocation models. We first show that asymmetric elastic loading characterizes the present Main Marmara Fault, a portion of the North Anatolian Fault along the northern margin of the Sea of Marmara. The ratio of asymmetry there is about 10. This ratio is even larger, about 30, along the northern Sumatra fault near lake Toba caldera. We then examine two profiles near Point Reyes and Point Arena across the northern San Andreas Fault that have been previously proposed as affected by asymmetry both in interseismic and coseismic effects. We show that an asymmetry ratio of 1.6 in interseismic loading exists near Point Arena, with the southwest side of the fault being more rigid than the northeast one. On the other hand, we do not find significant asymmetry for the Point Reyes profile that was previously described as highly asymmetric. We examine coseismic motion during the 1906 earthquake along the same two profiles. Ratios of 1.2 and 1.7 are found for the Point Arena and Point Reyes profiles, respectively. We discuss the possible causes of asymmetry. Contrasts in seismic velocity in the brittle portion suggest ratios generally not exceeding 2.5 for the dynamic rigidity in the upper brittle section. Larger ratios may involve other complex causes such as differences between static and dynamic rigidities, contrasts in rheology in the deeper creeping sections, and postseismic transients. We conclude that asymmetry should be systematically included within the parameters to be inverted when dealing with the mechanics of large‐scale strike‐slip faults.

Mesoscale Eddy Formation and Shock Features Associated with a Coastally Trapped Disturbance

Synoptic maps for 28-29 August 2002 indicate typical near-surface northerly flow along coastal California, while Goes-10 animated satellite imagery from this period show a stratuscapped, coastally trapped disturbance (CTD) propagating northward against the prevailing flow. A pronounced hydraulic-jump-like ('shock') feature develops in the cloud field south of Cape Mendocino (CM) and angles linearly away from the coast. Over the next /spl sim/6 hours both the CTD and the shock feature move northward and, as they approach the Cape, the leading edge of the CTD clouds roll-up into a visually striking cyclonic mesoscale eddy-with the shock feature being wrapped into the eddy. The CTD rather abruptly stalls and fails to round CM. Further, a second cyclonic mesoscale eddy is observed to form SW of Point Arena. Using a mesoscale model, many of the observed features of this case are forecast, including: (a) the cloud-filled, northward propagating CTD; (b) the development, linear structure, and orientation of the oblique shock feature; (c) the CTD rounds Point Arena, but fails to round CM; and (d) the formation of cyclonic mesoscale eddies near CM and Point Arena. The model fidelity permits us to analyze the dynamics associated with the shock feature and eddy formation.

Scatterometer and Model Wind and Wind Stress in the Oregon–Northern California Coastal Zone

Measurements of surface wind stress by the SeaWinds scatterometer on NASA's Quick Scatterometer (QuikSCAT) satellite are analyzed and compared with several different atmospheric model products, from an operational model and two high-resolution nested regional models, during two summer periods, June through September 2000 and 2001, in the coastal region west of Oregon and northern California. The mean summer wind stress had a southward component over the entire region in both years. Orographic intensifications of both the mean and fluctuating wind stress occurred near Cape Blanco, Cape Mendocino, and Point Arena. Substantial differences between the model products are found for the mean, variable, and diurnal wind stress fields. Temporal correlations with the QuikSCAT observations are highest for the operational model, and are not improved by either nested model. The highest-resolution nested model most accurately reproduced the mean observed stress fields, but slightly degrades the temporal correlations due to incoherent high-frequency (0.5–2 cpd) fluctuations. The QuikSCAT data reveal surprisingly strong diurnal fluctuations that extend offshore 150 km or more with magnitudes that are a significant fraction of the mean wind stress. Wind stress curl fields from QuikSCAT and the models show local cyclonic and anticyclonic maxima associated with the orographic wind intensification around the capes. The present results are consistent with the hypothesis of a wind-driven mechanism for coastal jet separation and cold water plume and anticyclonic eddy formation in the California Current System south of Cape Blanco.

The NEPA Book: A Step-by-Step Guide on How to Comply with the National Environmental Policy Act, 2nd Edition. Ronald E. Bass, Albert I. Herson, and Kenneth M. Bogdan. 2001. Solano Press Books, Point Arena, CA. 475 pp. $65 paperback.

"The NEPA Book: A Step-by-Step Guide on How to Comply with the National Environmental Policy Act, 2nd Edition. Ronald E. Bass, Albert I. Herson, and Kenneth M. Bogdan. 2001. Solano Press Books, Point Arena, CA. 475 pp. $65 paperback.." Environmental Practice, 5(4), pp. 382–383

Adjustment of the marine atmospheric boundary layer to the large‐scale bend in the California coast

Observations of the surface wind field off the U.S. West Coast were made from satellite by the Sea Surface Microwave/Imager (SSM/I) during June 1994 and June 1996. The coast bends inward 28° at 40° N latitude. Northerly wind speeds are high within a region that extends far south and offshore of this bend, bounded on the east by the California coast. On average, the high‐speed wind zone extends ∼250 km from shore and 800 km alongcoast. Long coast‐perpendicular aircraft transects show that moving onshore, the depth of the MABL decreases, the northerly wind speed increases, and the Froude number increases. A network of oceanographic buoys records the surface wind speed, direction, and pressure. From six buoy pressure measurements, the geostrophic wind vector was computed to represent the synoptic flow over the Oregon‐northern California coastal waters. The satellite surface wind fields were composited by the direction of the buoy geostrophic background wind. The predominant direction is 210°–180°. A high‐speed region extends south of the bend for directions in the 0°–180° range (moving counterclockwise), which corresponds to a downcoast component of the pressure gradient. For directions between 180° and 0°, flow splits at the bend and the region of highest winds is found to its north and offshore. A high‐speed region south of the bend was present in 65% of the satellite wind maps as well as in the June averages. The flow's response to coastal promontories such as Point Arena is nested within this broad zone of fast, thin, likely supercritical flow.

Past Earthquake-Induced Rapid Subsidence along the Northern San Andreas Fault: A Paleoseismological Method for Investigating Strike-Slip Faults

Evidence of rapid relative sea level changes preserved in sediment of coastal estuaries along the north coast segment of the San Andreas fault provides information on the dates of past earthquakes. This approach, although successfully used to document large subduction zone earthquakes, has not been used previously to constrain the dates of San Andreas fault or other strike-slip fault earthquakes. Data on prehistoric San Andreas fault earthquakes is needed for development of robust probabilistic hazard assessments in northern California and the San Francisco Bay area. Evidence of earthquake-induced subsidence is preserved in marshes at the northern margin of Bolinas Lagoon and the southeastern margin of Bodega Harbor. These sites occupy structural basins or troughs along the northern San Andreas fault. Radiocarbon dating and identification of the first occurrence of nonnative pollen near abrupt sedimentological changes in cores are used to constrain the dates of San Andreas fault earthquakes over about the last 800 years. Estuarine sediment from northern Bolinas Lagoon preserves evidence of an earthquake that occurred about 750 years ago. Evidence for this earthquake includes a marsh soil that was abruptly buried by tidal flat mud or coarse, poorly sorted deltaic deposits containing a mixture of terrestrial sediment and marine mud. Evaluation of diatom assemblages from above and below the buried soil horizon provides evidence of at least several decimeters of sustained relative sea level rise. Three buried soils in a marsh at the southern end of Bodega Harbor are likely a result of coseismic subsidence. All three buried marsh soils have abrupt upper contacts, although diatom evidence for decimeters of sustained subsidence is not as strong as it is for the buried soil in Bolinas Lagoon. Existing paleoseismic data on the northern San Andreas fault is compared with results of this study in order to evaluate the dates of prehistoric large earthquakes and length of past ruptures. These data indicate that an earthquake occurred about 400 years ago and another earthquake occurred about 700 years ago. The data allow for 1906-type ruptures of the fault from the Santa Cruz Mountains to at least Point Arena. However, a sequence of closely timed, smaller earthquakes would produce a similar set of paleoseismic data.

Shallow geometry and displacements on the San Andreas Fault near Point Arena based on trenching and 3‐D georadar surveying

To characterize buried portions of the San Andreas Fault (SAF) near its northern extremity in California, three trenches were excavated perpendicular to it and a 3‐D georadar data set was acquired. Similar sequences of unconsolidated fluvial sediments, Franciscan serpentinite and active fault zones were observed in the three trenches. Fault traces in the trenches were initially assumed to be part of a single SAF strand. However, the georadar data demonstrated the existence of two SAF strands, one of which was exposed in the central and southern trenches and the other in the northern trench. Offset of a linear‐trending georadar feature (possibly a fluvial paleochannel) suggests that 4.5–5.5 m of horizontal displacement occurred across the eastern SAF strand, either during the 1906 San Francisco earthquake or earlier. Georadar reflections from flat‐lying and trough‐shaped sedimentary boundaries are vertically offset by 0.2–0.3 m along both fault strands.

Phylogeography of the tidewater goby, Eucyclogobius newberryi (Teleostei, Gobiidae), in coastal California.

The tidewater goby, Eucyclogobius newberryi, inhabits discrete, seasonally closed estuaries and lagoons along approximately 1500 km of California coastline. This species is euryhaline but has no explicit marine stage, yet population extirpation and recolonization data suggest tidewater gobies disperse intermittently via the sea. Analyses of mitochondrial control region and cytochrome b sequences demonstrate a deep evolutionary bifurcation in the vicinity of Los Angeles that separates southern California populations from all more northerly populations. Shallower phylogeographic breaks, in the vicinities of Seacliff, Point Buchon, Big Sur, and Point Arena segregate the northerly populations into five groups in three geographic clusters: the Point Conception and Ventura groups between Los Angeles and Point Buchon, a lone Estero Bay group from central California, and San Francisco and Cape Mendocino groups from northern California. The phylogenetic relationships between and patterns of molecular diversity within the six groups are consistent with repeated, and sometimes rapid, northward and southward range expansions out of central California caused by Quaternary climate change. Plio-Pleistocene tectonism, Quaternary coastal geography and hydrography, and historical human activities probably also influenced the modern geographic and genetic structure of E. newberryi. The phylogeography of E. newberryi is concordant with phylogeographic patterns in several other coastal California taxa, suggesting common extrinsic factors have had similar effects on different species. However, there is no evidence of a phylogeographic break coincident with a biogeographic boundary at Point Conception.