California Borderland Research Articles

Composition of Dissolved Organic Matter in Pore Waters of Anoxic Marine Sediments Analyzed by 1H Nuclear Magnetic Resonance Spectroscopy

Marine sediments are globally significant sources of dissolved organic matter (DOM) to the oceans, but the biogeochemical role of pore-water DOM in the benthic and marine carbon cycles remains unclear due to a lack of understanding about its molecular composition. To help fill this knowledge gap, we used 1H nuclear magnetic resonance (NMR) spectroscopy to examine depth variability in the composition of pore-water DOM in anoxic sediments of Santa Barbara Basin, California Borderland. Proton detected spectra were acquired on whole samples without pre-concentration to avoid preclusion of any DOM components from the analytical window. Broad unresolved resonance (operationally assigned to carboxyl-rich alicyclic molecules, or CRAM) dominated all spectra. Most of the relatively well-resolved peaks (attributed to biomolecules or their derivatives) appeared at chemical shifts similar to those previously reported for marine DOM in the literature, but at different relative intensities. DOM composition changed significantly within the top 50 cm of the sediment column, where the relative intensity of CRAM increased, and the relative intensity of resolved resonances decreased. The composition of CRAM itself also changed throughout the entire length of the 4.5-m profile, as CRAM protons became increasingly aliphatic at the expense of functionalized protons. Given that pore-water DOM is generated from sedimentary organic matter that includes pre-aged and degraded material, and that DOM could theoretically be subjected to microbial reworking in the pore waters for centuries to millennia, these data suggest that marine sediments may be sources of CRAM that are compositionally unique from CRAM generated in the upper ocean.

Bottom-water oxygenation and environmental change in Santa Monica Basin, Southern California during the last 23 kyr

The Southern California Borderland is a region that experiences strong natural variations in bottom water oxygen and pH. We use marine sediments from Santa Monica Basin to reconstruct environmental conditions in the basin's bottom water from the Last Glacial Maximum (LGM) to present. We then compare the records to the adjacent Santa Barbara Basin and Santa Lucia Slope. High-resolution records of benthic foraminiferal oxygen and carbon isotopes (δ18O and δ13C), benthic foraminiferal assemblages, and bulk sedimentary organic matter geochemistry records exhibit major changes associated with late Quaternary millennial-scale global climate oscillations. Our data show the dominance of low‑oxygen benthic foraminiferal assemblages during warm intervals, and assemblages representing higher dissolved oxygen during cooler intervals, as also seen in Santa Barbara Basin and Santa Lucia Slope. However, our record shows a stronger and longer-lasting oxygen minimum zone (OMZ) between the mid Younger Dryas (YD) and the Early Holocene than at neighboring sites, indicated by dominance of Bolivina tumida (characteristic of major hypoxia) in the assemblage. The middle to late Holocene (from ~9 to 0kyr) had weaker hypoxia than the early Holocene, with assemblages mainly composed of Bolivina argentea and Uvigerina peregrina. Santa Monica Basin remained slightly hypoxic throughout the past 23kyr, however, differences in the degree of hypoxia from Santa Barbara Basin and Santa Lucia Slope (especially from the B-A to the Early Holocene) are seen. The Santa Monica Basin bottom water is affected by regional processes, such as changes in the source of intermediate water and/or changing ventilation (oxygenation) of the intermediate water source. This is due to the greater depth and the more southern geographic position of the Basin, which reduces exposure to the oxygenated North Pacific Intermediate Water current. Additional local processes also affect the basin, such as the effects of sediment influx from submarine canyons. This analysis utilizing parallel geochemical and micropaleontological records brings new insights into bottom water and climate conditions in Santa Monica Basin, indicating regional similarities and differences from adjacent basins, and provides insight into the causes for changes in bottom water oxygenation.

Ecophenotypic responses of benthic foraminifera to oxygen availability along an oxygen gradient in the California Borderland

AbstractSpatial variation in environmental conditions can elicit predictable size and morphological responses in marine organisms through influences on physiology. Thus, spatial and temporal variation in marine organism size and shape are often used to infer paleoenvironmental conditions, such as dissolved oxygen concentrations. Benthic foraminifera commonly serve as a tool for reconstructing past ocean oxygen levels. For example, benthic foraminiferal species assemblages, within‐ and among‐species patterns of test morphology, and geochemical analyses of carbonate tests are often employed to reconstruct past marine conditions. In this study, we measured the sizes and shapes of modern foraminifera representing four species that inhabit a steep oxygen gradient in the Santa Monica Basin on the Southern California Borderland with the aim of quantifying the influence of oxygen availability on foraminiferal morphology, both within and among species. Most foraminifera rely on aerobic respiration, but the four benthic foraminifera from the Santa Monica Basin do not show the predicted size and morphological responses to variations in dissolved oxygen concentrations based on first principles of cell physiology: Bolivina spissa shows no volume or volume‐to‐surface area response, Uvigerina peregrina increases in both test volume and volume‐to‐surface area ratio with decreasing dissolved oxygen concentrations, and both Bolivina argentea and Loxostomum pseudobeyrichi decrease in test volume, but only L. pseudobeyrichi shows a decrease in test volume‐to‐surface area ratio with decreasing oxygen concentrations as expected from physiological predictions. These findings imply that the morphological responses of individual foraminiferal species are not necessarily representative of the responses of other foraminiferal species within the community. Our findings further suggest that these species use physiological strategies such as depressed metabolic rates and alternative energy metabolisms to persist in low oxygen environments and, therefore, cannot be used in any simple way as paleo‐oxygen indicators. Should Proterozoic (1,000–542 million years ago) protists have possessed metabolic strategies similar to foraminifera, the sizes and shapes of protists in the fossil record may not usefully constrain ambient oxygen conditions during the appearance and initial taxonomic radiation of heterotrophic eukaryotes.

Review: Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940 by Benny J. Andrés, Jr.

Review: Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940 by Benny J. Andrés, Jr.

Recycling of Organic Matter in the Sediments of Santa Monica Basin, California Borderland

Geochemical and isotopic data for the uppermost 1.2 m of the sediments of the central Santa Monica Basin plain were examined to better understand organic matter deposition and recycling at this site. Isotopic signatures (Δ14C and δ13C) of methane (CH4) and dissolved inorganic carbon (DIC) indicate the occurrence of anaerobic oxidation of CH4 that is fueled by CH4 supplied from a relict reservoir that is decoupled from local organic carbon (Corg) degradation and methanogenesis. This finding was corroborated by a flux budget of pore-water solutes across the basal horizon of the profile. Together these results provide a plausible explanation for the anomalously low ratio between alkalinity production and sulfate consumption reported for these sediments over two decades ago. Shifts in Δ14C and δ13C signatures of Corg have previously been reported across the 20-cm depth horizon for this site and attributed to a transition from oxic to anoxic bottom water that occurred ~350 years BP. However, we show that this horizon also coincides with a boundary between the base of a hemipelagic mud section and the top of a turbidite interval, complicating the interpretation of organic geochemical data across this boundary. Radiocarbon signatures of DIC diffusing upward into surface sediments indicate that remineralization at depth is supported by relatively 14C-enriched Corg within the sedimentary matrix. While the exact nature of this Corg is unclear, possible sources are hemipelagic mud sections that were buried rapidly under thick turbidites, and 14C-rich moieties dispersed within Corg-poor turbidite sections.

Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940. By Benny J. Andres Jr. College Station: Texas A&M University Press, 2015. xv + 229 pp. Illustrations, notes, bibliography, and index. Cloth $43.00.

<i> Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940</i>. By Benny J. Andres Jr. College Station: Texas A&amp;M University Press, 2015. xv + 229 pp. Illustrations, notes, bibliography, and index. Cloth $43.00.

Records of continental slope sediment flow morphodynamic responses to gradient and active faulting from integrated AUV and ROV data, offshore Palos Verdes, southern California Borderland

Variations in seabed gradient are widely acknowledged to influence deep-water deposition, but are often difficult to measure in sufficient detail from both modern and ancient examples. On the continental slope offshore Los Angeles, California, autonomous underwater vehicle, remotely operated vehicle, and shipboard methods were used to collect a dense grid of high-resolution multibeam bathymetry, chirp sub-bottom profiles, and targeted sediment core samples that demonstrate the influence of seafloor gradient on sediment accumulation, depositional environment, grain size of deposits, and seafloor morphology. In this setting, restraining and releasing bends along the active right-lateral Palos Verdes Fault create and maintain variations in seafloor gradient. Holocene down-slope flows appear to have been generated by slope failure, primarily on the uppermost slope (~100–200m water depth). Turbidity currents created a low relief (<10m) channel, up-slope migrating sediment waves (λ=~100m, h≤2m), and a series of depocenters that have accumulated up to 4m of Holocene sediment. Sediment waves increase in wavelength and decrease in wave height with decreasing gradient. Integrated analysis of high-resolution datasets provides quantification of morphodynamic sensitivity to seafloor gradients acting throughout deep-water depositional systems. These results help to bridge gaps in scale between existing deep-sea and experimental datasets and may provide constraints for future numerical modeling studies.

Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940

Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940

Organic matter cycling across the sulfate-methane transition zone of the Santa Barbara Basin, California Borderland

Consumption of sulfate (SO42−) in the sulfate-methane transition zone (SMTZ) has often been considered to be due solely to anaerobic oxidation of methane (AOM). However, recent studies show SO42− fluxes into the SMTZ that exceed methane (CH4) fluxes, thereby challenging this conceptual model. Co-occurrence of organoclastic SO42− reduction (oSR) with AOM in the SMTZ has been hypothesized to be the cause for this flux imbalance, but conclusive evidence is lacking. To address this knowledge gap, we investigated organic matter cycling in the SMTZ of the organic-rich sediments of the Santa Barbara Basin, California Borderland, and examined the occurrence of oSR within this zone using bulk solute profiles and Δ14C and δ13C values of selected carbon pools. We also tested the hypothesis that the SMTZ acts as an oxidation front not just for CH4, but also for dissolved organic carbon (DOC) that is produced below the SMTZ and migrates upward. Mass balance calculations for the SMTZ based on reaction stoichiometry and Δ14C and δ13C values of associated carbon fluxes indicate that ∼35–45% of total SO42− reduction in the SMTZ occurs via oSR, with the remainder attributable to AOM. The δ13C value of net DOC production is distinct from that of the fraction of bulk POC undergoing degradation, suggesting that pore-water DOC represents a compositionally unique slice of the metabolizable POC pool. DOC diffusing upward at 450cm is virtually free of 14C and contain low levels of short-chain organic acids. Radiocarbon mass balance shows that >30% of this pre-aged, and presumably refractory, DOC is removed from the pore waters within or immediately below the SMTZ. Although the SMTZ does not appear to be a major net DOC oxidation front, these results show that DOC dynamics provide unique insights into organic matter processing in these subsurface sediments.

Review: Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940 by Benny J. Andrés

Book Review| November 01 2015 Review: Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940 by Benny J. Andrés Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940. By Benny J. Andrés. (College Station: Texas A&M University, 2015, 288 pp. $43.00 cloth.) Douglas C. Sackman Douglas C. Sackman Douglas C. Sackman, the James Dolliver Professor of History at the University of Puget Sound, is the author of Orange Empire: California and the Fruits of Eden and is currently writing a book entitled American Panorama: Rediscovering the History of the North American West. Search for other works by this author on: This Site PubMed Google Scholar Southern California Quarterly (2015) 97 (4): 424–427. https://doi.org/10.1525/ucpsocal.2015.97.4.424 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Search Site Citation Douglas C. Sackman; Review: Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940 by Benny J. Andrés. Southern California Quarterly 1 November 2015; 97 (4): 424–427. doi: https://doi.org/10.1525/ucpsocal.2015.97.4.424 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentSouthern California Quarterly Search This content is only available via PDF. © 2015 by The Historical Society of Southern California2015 Article PDF first page preview Close Modal You do not currently have access to this content.

Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940

Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900–1940

Demasking multiple artifact in crustal seismic images from marine reflection data in the southern california borderland

Marine seismic reflection surveys are often masked by strong water-bottom multiples that limit the use of data beyond the first multiple waves. In this study, we have successfully suppressed much of the multiple artifacts in the depth images of two of the marine seismic reflection profiles from the Los Angeles regional seismic experiment (LARSE) by applying reverse time migration (RTM). In contrast to most seismic reflection methods that use only primary reflections and diffractions, the two-way RTM migrates both primaries and multiple reflections to their places of origination: seabed multiples to the sea bottom and primaries to the reflecting interfaces. Based on the RTM depth sections of LARSE lines 1 and 2, we recognize five stratigraphic units from the sea bottom to a depth of 6 km. These units are Pliocene and younger strata, probably Miocene syntectonic strata, two deeper sequences of unknown age and lithology as well as Miocene volcanic layers on Catalina ridge. Several inferred igneous intrusions in the upper crust comprise a sixth unit. The existence of a thick sedimentary section in the Catalina Basin, which might include Paleogene and Cretaceous fore-arc strata, has important geologic significance. If borne out by further studies, significant revisions of current structural and stratigraphic interpretations of the California borderland would be warranted.

Late Miocene–Quaternary fault evolution and interaction in the southern California Inner Continental Borderland

Changing conditions along plate boundaries are thought to result in the reactivation of preexisting structures. The offshore southern California Borderland has undergone dramatic adjustments as conditions changed from subduction tectonics to transform tectonics, including major Miocene oblique extension, followed by transpressional fault reactivation. However, consensus is still lacking about stratigraphic age models, fault geometry, and slip history for the near-offshore area between southern Los Angeles and San Diego (California, USA). We interpret an extensive data set of seismic reflection, bathymetric, and stratigraphic data from that area to determine the three-dimensional geometry and kinematic evolution of the faults and folds and document how preexisting structures have changed their activity and type of slip through time. The resulting structural representation reveals a moderately landward-dipping San Mateo–Carlsbad fault that converges downward with the steeper, right-lateral Newport-Inglewood fault, forming a fault wedge affected by Quaternary contractional folding. This fault wedge deformed in transtension during late Miocene through Pliocene time. Subsequently, the San Mateo–Carlsbad fault underwent 0.6–1.0 km displacement, spatially varying between reverse right lateral and transtensional right lateral. In contrast, shallow parts of the previously identified gently dipping Oceanside detachment and the faults above it appear to have been inactive since the early Pliocene. These observations, together with new and revised geometric representations of additional steeper faults, and the evidence for a pervasive strike-slip component on these nearshore faults, suggest a need to revise the earthquake hazard estimates for the coastal region.

Transpressional segment boundaries in strike‐slip fault systems offshore southern California: Implications for fluid expulsion and cold seep habitats

AbstractThe importance of tectonics and fluid flow in controlling cold seep habitats has long been appreciated at convergent margins but remains poorly understood in strike‐slip systems. Here we present geophysical, geochemical, and biological data from an active methane seep offshore from Del Mar, California, in the inner California borderlands (ICB). The location of this seep appears controlled by localized transpression associated with a step in the San Diego Trough fault zone and provides an opportunity to examine the interplay between fluid expulsion and restraining step overs along strike‐slip fault systems. These segment boundaries may have important controls on seep locations in the ICB and other margins characterized by strike‐slip faulting (e.g., Greece, Sea of Marmara, and Caribbean). The strike‐slip fault systems offshore southern California appear to have a limited distribution of seep sites compared to a wider distribution at convergent plate boundaries, which may influence seep habitat diversity and connectivity.

Generating archeal diversity

Subsurface Microbes Retroelements—gene sequences that are introduced into DNA through an RNA intermediate—in subsurface archaea help increase gene and protein diversity. Paul et al. identified an archeal virus from a methane seep in a California borderlands basin that contains a complete and active diversity-generating retroelement (DGR). Furthermore, published metagenomes of two uncultivated nanoarchaea from the marine subsurface contain at least four DGRs, more than any other bacteria or virus known to date. Because anaerobic archaea in the subsurface grow so slowly, and thus have low background genome mutations, DGRs may be a widespread source of genetic diversity in these environments. Nat. Comm. 10.1038/ncomms7585 (2015).

Power and control in the Imperial Valley: nature, agribusiness, and workers on the California borderland, 1900-1940

Benny J. Andres, Jr., Power and Control in the Imperial Valley: Nature, Agribusiness, and Workers on the California Borderland, 1900-1940. Reviewed by Nathan F. Sayre, University of California, Berkeley The Imperial Valley, straddling the United States-Mexico border from the mouth of the Colorado River north into California, must be considered one of the most extraordinary cases of agro-industrial transformation in the world. Benny Andres, Jr. has produced a remarkably detailed chronicle of this world historic transformation, based on a wealth of primary materials. He condenses the period from 1900 to 1940 into just 161 pages, followed by a short Afterword that considers this history from the perspective of the present, when “the Imperial Valley is infamous for its flagrant water waste, unsustainable farming practices, feeble economic output, endemic poverty, and debilitating pollution” (p. 163). “Imperial-Mexicali Valley’s history,” Andres argues, “is the quest for power, control, and profits” (p. 66), reflecting “a peculiar mental inclination” (p. 4) to dominate and exploit nature and people alike. He shows how an unholy alliance of capitalists, landowners and politicians, increasingly enabled by government policies and largesse at all levels, conquered one of the hottest and driest places in North America by means of irrigation, agricultural science, chemical pesticides, legal- bureaucratic chicanery and outright violence. Moving in broadly chronological fashion, Andres explores how the Colorado River was diverted to irrigate the valley (chapter 1); how soils, plants, insects and animals were forcibly manipulated and persecuted to produce ever more crops (chapter 2); how racist ideologies and tactics were mobilized and resisted in creating strict (if also dynamic) hierarchies of social domination (chapters 3 and 4); and how all of these transformations shaped four decades of brutal repression of farm labor organizers, activists and advocates (chapter 5). The strength of Power and Control in the Imperial Valley rests on the fine grain of its empirical materials, ranging from the engineering of groundwater drainage and salinity control to the cross-border micro-politics of the Mexican Revolution. Specific details enrich the narrative throughout, bringing an almost visceral quality to droughts, floods, farming practices, police and vigilante violence, perverted justice and contorted logic. Although the diversion of the Colorado River has received comparably detailed treatments before, to my knowledge no one has chronicled the region’s social history so richly until now. It is a daunting task to fit so much detail into such a short book, however. Within each chapter, events twist and turn so quickly, with so many causal and contingent factors invoked or alluded to, that basic facts sometimes become elusive. How much were farm wages over this period? Were they paid by the hour or the day? How often were they paid at all? More tables and maps would be helpful. Similarly, the chapters

Records of past mid-depth ventilation: Cretaceous ocean anoxic event 2 vs. Recent oxygen minimum zones

Abstract. Present day oceans are well ventilated, with the exception of mid-depth oxygen minimum zones (OMZs) under high surface water productivity, regions of sluggish circulation, and restricted marginal basins. In the Mesozoic, however, entire oceanic basins transiently became dysoxic or anoxic. The Cretaceous ocean anoxic events (OAEs) were characterised by laminated organic-carbon rich shales and low-oxygen indicating trace fossils preserved in the sedimentary record. Yet assessments of the intensity and extent of Cretaceous near-bottom water oxygenation have been hampered by deep or long-term diagenesis and the evolution of marine biota serving as oxygen indicators in today's ocean. Sedimentary features similar to those found in Cretaceous strata were observed in deposits underlying Recent OMZs, where bottom-water oxygen levels, the flux of organic matter, and benthic life have been studied thoroughly. Their implications for constraining past bottom-water oxygenation are addressed in this review. We compared OMZ sediments from the Peruvian upwelling with deposits of the late Cenomanian OAE 2 from the north-west African shelf. Holocene laminated sediments are encountered at bottom-water oxygen levels of &lt; 7 μmol kg−1 under the Peruvian upwelling and &lt; 5 μmol kg−1 in California Borderland basins and the Pakistan Margin. Seasonal to decadal changes of sediment input are necessary to create laminae of different composition. However, bottom currents may shape similar textures that are difficult to discern from primary seasonal laminae. The millimetre-sized trace fossil Chondrites was commonly found in Cretaceous strata and Recent oxygen-depleted environments where its diameter increased with oxygen levels from 5 to 45 μmol kg−1. Chondrites has not been reported in Peruvian sediments but centimetre-sized crab burrows appeared around 10 μmol kg−1, which may indicate a minimum oxygen value for bioturbated Cretaceous strata. Organic carbon accumulation rates ranged from 0.7 and 2.8 g C cm−2 kyr−1 in laminated OAE 2 sections in Tarfaya Basin, Morocco, matching late Holocene accumulation rates of laminated Peruvian sediments under Recent oxygen levels below 5 μmol kg−1. Sediments deposited at &gt; 10 μmol kg−1 showed an inverse exponential relationship of bottom-water oxygen levels and organic carbon accumulation depicting enhanced bioirrigation and decomposition of organic matter with increased oxygen supply. In the absence of seasonal laminations and under conditions of low burial diagenesis, this relationship may facilitate quantitative estimates of palaeo-oxygenation. Similarities and differences between Cretaceous OAEs and late Quaternary OMZs have to be further explored to improve our understanding of sedimentary systems under hypoxic conditions.

Dissolved organic carbon dynamics in anaerobic sediments of the Santa Monica Basin

Cycling of dissolved organic carbon (DOC) was investigated in anoxic sediments of the Santa Monica Basin, California Borderland, by analyzing the concentration and isotopic signatures (Δ14C and δ13C) of pore-water DOC and dissolved inorganic carbon (DIC), and organic compound classes extracted from the bulk sediments. DOC and DIC increased across the sediment–water interface, indicating net efflux of these solutes out of the sediments. Throughout the depth interval examined (0–30cm), the Δ14C value of DOC (Δ14CDOC) was similar to, or higher than, that of bulk sedimentary particulate organic carbon (POC), indicating degradation of relatively 14C-rich components of POC. There were prominent peaks in both Δ14CDOC and Δ14CDIC in the uppermost 2 cm of the sediment column, indicating degradation and remineralization of 14C-rich, labile organic matter in the near-surface sediments. However, below these sub-surface maxima, Δ14CDOC and Δ14CDIC decreased with depth by ∼200‰ and ∼50‰, respectively. Given the diffusive time scales, these decreases were too large to be explained by 14C loss due to radioactive decay. To help explain these observations, we constructed and implemented a selective degradation model that considers bulk pore-water DOC to be the sum of three kinetically- and isotopically-distinct sub-components. Based on this model, the most reactive DOC fraction, which supported ∼60% of the DIC production, had a Δ14C value indicating the presence of bomb-14C. The intermediate fraction had a Δ14C value of ∼−60‰ and accounted for most of the pore-water DOC standing stock. The least reactive fraction was virtually non-reactive in these sediments, and had a Δ14C value of ∼−500‰. The benthic DOC flux of this 14C-depleted, poorly-reactive DOC fraction may represent a source of pre-aged, refractory DOC to the oceans.

Slip Rate on the San Diego Trough Fault Zone, Inner California Borderland, and the 1986 Oceanside Earthquake Swarm Revisited

The San Diego trough fault zone (SDTFZ) is part of a 90-km-wide zone of faults within the inner California Borderland that accommodates motion between the Pacific and North American plates. Along with most faults offshore southern California, the slip rate and paleoseismic history of the SDTFZ are unknown. We pre- sent new seismic reflection data that show that the fault zone steps across a 5-km-wide stepover to continue for an additional 60 km north of its previously mapped extent. The 1986 Oceanside earthquake swarm is located within the 20-km-long restraining stepover. Farther north, at the latitude of Santa Catalina Island, the SDTFZ bends 20° to the west and may be linked via a complex zone of folds with the San Pedro basin fault zone (SPBFZ). In a cooperative program between the U.S. Geological Survey (USGS) and the Monterey Bay Aquarium Research Institute (MBARI), we measure and date the coseismic offset of a submarine channel that intersects the fault zone near the SDTFZ-SPBFZ junction. We estimate a horizontal slip rate of about 1:5 0:3 mm=yr over the past 12,270 yr.

Conservation Outcomes and Social Relations: A Comparative Study of Private Ranchland Conservation Easements

Conservation easements have increased dramatically but their social and ecological outcomes are largely unknown. To examine the influence of social relations and institutional structure on easement design and conservation outcomes, we compared two regions where land trusts hold conservation easements protecting large areas of private rangeland: Lassen Foothills, California, and Malpai Borderlands, Arizona and New Mexico. We conducted interviews with landowners, land trust staff, and public agency employees, and analyzed easement documents and monitoring reports. Social relations and organization goals influenced easement terms and their direct effects on land use. Furthermore, easements had important indirect conservation-relevant outcomes resulting from increased land management resources, financial incentives, and altered relations among landowners, government agencies, and nongovernmental organizations (NGOs). Easements entail a combination of collaborative and regulatory approaches, and their embedded social relations are important for conservation outcome assessment. These findings have significant implications for how conservation programs are designed, monitored, enforced, and evaluated.