Geology topics

Research about California

Source-linked reports with geographic coverage including California.

At least 361 records · Page 20Linked to original sources

USGS2024

Probabilistic assessment of postfire debris-flow inundation in response to forecast rainfall

Communities downstream of burned steep lands face increases in debris-flow hazards due to fire effects on soil and vegetation. Rapid postfire hazard assessments have traditionally focused on quantifying spatial variations in debris-flow likelihood and volume in response to design rainstorms. However, a methodology that provides estimates of debris-flow inundation downstream of burned areas based on forecast rainfall would provide decision-makers with information that directly addresses the potential for downstream impacts. We introduce a framework that integrates a 24 h lead-time ensemble precipitation forecast with debris-flow likelihood, volume, and runout models to produce probabilistic maps of debris-flow inundation. We applied this framework to simulate debris-flow inundation associated with the 9 January 2018 debris-flow event in Montecito, California, USA. When the observed debris-flow volumes were used to drive the probabilistic forecast model, analysis of the simulated inundation probabilities demonstrates that the model is both reliable and sharp. In the fully predictive model, however, in which debris-flow likelihood and volume were computed from the atmospheric model ensemble's predictions of peak 15 min rainfall intensity, I 15 , the model generally under-forecasted the inundation area. The observed peak I 15 lies in the upper tail of the atmospheric model ensemble spread; thus a large fraction of ensemble members forecast lower I 15 than observed. Using these I 15 values as input to the inundation model resulted in lower-than-observed flow volumes which translated into under-forecasting of the inundation area. Even so, approximately 94 % of the observed inundated area was forecast to have an inundation probability greater than 1 %, demonstrating that the observed extent of inundation was generally captured within the range of outcomes predicted by the model. Sensitivity analyses indicate that debris-flow volume and two parameters associated with debris-flow mobility exert significant influence on inundation predictions, but reducing uncertainty in postfire debris-flow volume predictions will have the largest impact on reducing inundation outcome uncertainty. This study represents a first step toward a near-real-time hazard assessment product that includes probabilistic estimates of debris-flow inundation and provides guidance for future improvements to this and similar model frameworks by identifying key sources of uncertainty.

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USGS2024

Pesticide concentrations of surface water and suspended sediment in Yolo By-Pass and Cache Slough Complex, California, 2019–2021

Managed flow pulses in the north Sacramento-San Joaquin Delta are an adaptive management tool used in efforts to enhance food availability in delta smelt ( Hypomesus transpacificus ) habitat as part of the North Delta Food Subsidies Action. The California Department of Water Resources (DWR) monitors non-managed seasonal and local flow pulses and managed flow pulses from agricultural drainage or main stem Sacramento River water redirected through Yolo By-Pass. Augmented flow pulses are hypothesized to improve net positive flow during summer and fall in Yolo By-Pass and enhance plankton availability in delta smelt habitat in Cache Slough complex. However, flow pulses may also result in unintended negative effects of increased pesticides that are transported through Yolo By-Pass. Here, we evaluate pesticides in surface water and suspended sediment correlated with flow pulses in Yolo By-Pass during the 2019–21 calendar years. Surface-water and suspended-sediment samples were collected by DWR personnel. Water samples were analyzed at the U.S. Geological Survey Organic Chemistry Research Laboratory in Sacramento, California, for a suite of as many as 178 current-use pesticides and pesticide degradates using gas chromatography with mass spectrometry (GC/MS), gas chromatography with tandem mass spectrometry, and liquid chromatography with tandem mass spectrometry. Suspended sediments filtered from water samples were analyzed for a suite of as many as 173 current-use pesticides and pesticide degradates. There were 52 different current-use pesticides and pesticide degradates detected in water samples collected throughout the study. Concentrations ranged from below method detection limits to 4,070 nanograms per liter. Five different compounds in water samples were detected with concentrations above U.S. Environmental Protection Agency aquatic life benchmarks. In suspended-sediment samples collected throughout the study, eight different current-use pesticides and pesticide degradates were detected. Total pesticide concentrations were highest at surface-water sites in the northern end of Yolo By-Pass and decreased farther downstream during the same sampling events. Total pesticide concentrations generally were higher for most surface-water sites immediately before or during the managed flow pulse in 2019 versus after the flow pulse. Finally, mean total pesticide concentrations for each surface-water site generally were higher during all of 2019 than 2021, regardless of sampling period.

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USGS2024

Effects of 2D hydrodynamic model resolution on habitat estimates for rearing Coho Salmon in contrasting channel forms

Estimating the impacts of water allocation decisions on fish populations and habitat availability is an important part of environmental flow assessments, especially in locations where water resources are limited. Two-dimensional hydrodynamic models (2DHMs) are commonly coupled with biological models to estimate fish habitat quality, area, and capacity across a range of proposed streamflows. Increasingly, resource managers are relying on landscape-scale model domains with coarse model resolutions to maintain feasible computational loads, but this may affect habitat estimates if the mesh element size of the model exceeds the spatial scale relevant to the organism. We investigated how coarsening the resolution of a 2DHM influences the area and spatial distribution of estimated Coho Salmon ( Oncorhynchus kisutch ) fry habitats. We used an interpolation scheme that upscaled mesh elements from a high-resolution (0.25 m 2 ) 2DHM to quantify and visualize the effects of 2DHM resolution on estimates of Coho Salmon fry habitat for two contrasting channel morphologies and across a broad range of streamflows. Estimates of Coho Salmon fry habitat at increasingly coarser resolutions led to 20%–50% reductions in weighted usable habitat area (WUA) across several streamflow scenarios for a complex channel type, but did not impact estimates in a confined, flume-like channel. Additionally, flow-to-habitat area relationships were not congruent at a given streamflow when resolution coarsened. Along with almost 500% more high-quality habitat area estimated in the complex channel type over the confined, discrepancies in habitat area increased with higher flows in areas defined as optimal for rearing Coho Salmon fry. Considering that complex channel types contain critical habitat for Coho Salmon fry, this study suggests coarse 2DHM resolutions may exclude important wetted edge and off-channel habitats from environmental flow assessments.

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USGS2024

Rangewide occupancy of a flagship species, the Coastal California Gnatcatcher (Polioptila californica californica) in southern California: Habitat associations and recovery from wildfire

The Coastal California Gnatcatcher ( Polioptila californica californica ), a federally threatened species, is a flagship species for regional conservation planning in southern California (USA). An inhabitant of coastal sage scrub vegetation, the gnatcatcher has declined in response to habitat loss and fragmentation, exacerbated by catastrophic wildfires. We documented the status of gnatcatchers throughout their California range and examined post-fire recovery of gnatcatchers and their habitat. We used GIS to develop a habitat suitability model for Coastal California Gnatcatchers using climate and topography covariates and selected over 700 sampling points in a spatially balanced manner. Bird and vegetation data were collected at each point between March and May in 2015 and 2016. Presence/absence of gnatcatchers was determined during three visits to points, using area searches within 150 x 150 m plots. We used an occupancy framework to generate Percent Area Occupied (PAO) by gnatcatchers, and analyzed PAO as a function of time since fire. At the regional scale in 2016, 23% of the points surveyed were occupied by gnatcatchers, reflecting the effect of massive wildfires in the last 15 years. Similarly, PAO in the post-fire subset of points was 24%, with the highest occupancy in unburned (last fire <2002) habitat. Positive predictors of occupancy included percent cover of California sagebrush ( Artemisia californica ), California buckwheat ( Eriogonom fasciculatum ), and sunflowers ( Encelia spp., Bahiopsis laciniata ), while negative predictors included laurel sumac ( Malosma laurina ) and total herbaceous cover; in particular, non-native grasses. Our findings indicate that recovery from wildfire may take decades, and provide information to speed up recovery through habitat restoration.

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USGS2024

A comparative analysis of OpenET for evaluating evapotranspiration in California almond orchards

The almond industry in California faces water management challenges that are being exacerbated by droughts, climate change, and groundwater sustainability legislation. The Tree-crop Remote sensing of Evapotranspiration eXperiment (T-REX) aims to explore opportunities to improve precision irrigation management for woody perennial cropping systems. Almond orchards in the California Central Valley were equipped with eddy covariance flux measurements to evaluate satellite remote sensing-based evapotranspiration (RSET) models. OpenET provides high-resolution (30-m spatial and daily temporal) RSET data, synthesizing decades of research for practical water management. This study provides an evaluation of OpenET performance at six almond sites covering a large range in soils, age, and variety. It also compares OpenET ensemble evapotranspiration (ET) data with applied irrigation and precipitation records over an additional 148 almond orchards located in the Central Valley of California. Results show OpenET models, including the ensemble ET value, produced reasonable and actionable ET values, with overall coefficient of determination (R 2 ) and mean absolute error values of 0.73- and 0.95-mm d −1 at the daily time step, respectively. However, given the temporal sampling of Landsat (8-day revisit) and the interpolation methods used, the assessed ET models had difficulty in capturing short-term variability in almond ET; for example, the rapid decline in measured ET observed as a response to lack of irrigation preceding and during almond harvest. The study also drew attention to the spatial complexity in scenarios where irrigated orchards are surrounded by hot/dry areas, causing discrepancies between measured and modeled ET values. In comparison with irrigation records, OpenET ensemble ET was capable of quantifying water input (applied irrigation + precipitation) in almond orchards to within 13 % when evaluating monthly data. Initial results presented here reinforce the idea that RSET models, such as in OpenET, are powerful tools, yet their application requires nuanced understanding and careful consideration of local conditions.

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USGS2024

An integrated analysis for estimation of survival, growth, and movement of unmarked juvenile anadromous fish

Managers invest substantial resources to promote recovery of declining anadromous fish stocks. Recovery strategies are manifold and often include management actions intended to stimulate somatic growth, increase in-river survival, and motivate juvenile outmigration during favorable environmental conditions. Evaluating the efficacy of these management actions is difficult, however, because monitoring data that explicitly track individuals from egg deposition to juvenile outmigration are typically lacking. We developed an integrated population model that links two different and often collected types of anadromous fish monitoring data: spawning ground surveys and rotary screw trap juvenile catch data. The integrated model accounts for incomplete detection and uses the two sources of data to estimate juvenile demographic parameters in a multistate framework. We evaluated the model's performance using simulated data under a range of conditions typically encountered in similar surveys. Simulation results indicated that the model estimated juvenile survival, growth, and movement with no-to-minimal bias (i.e., ≥ 50 % of simulations ± 0–0.05). As an example case study, we fit the model to empirical fall-run Chinook Salmon ( Oncorhynchus tshawytscha ) monitoring data collected in California's Central Valley, U.S.A. In doing so, we evaluated the influence of environmental conditions (e.g., discharge, water temperature) and habitat availability on juvenile demographic rates. We demonstrated that through our integrated approach we could estimate state transition probabilities that are typically inestimable for naturally produced, unmarked juvenile fish when using traditional statistical approaches to analyze these types of monitoring data. Furthermore, the structure of our model can serve as a useful foundation for decision-support models within adaptive management programs by directly linking management actions, decision-support-model predictions, and monitoring.

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USGS2024

Characteristics of the fault damage zone From high-resolution seismic imaging along the Palos Verdes Fault, California

The distribution and intensity of fault damage zones provides insight into fault activity and its relationship to fluid flow in the crust. Presently, measures of the in-situ distribution of fault damage remain limited and along-strike studies are rare. This study focuses on an offshore section Palos Verdes Fault damage zone that spans 28 km, near Los Angeles, California. To investigate the previously unresolved shallow (∼400 m below the seafloor) fault damage zone we use densely spaced (∼500 m line separation) newly collected sparker multichannel seismic lines and sub-bottom profiles. The combination of high-resolution acquisition methods and specialized seismic processing workflows provide improved imaging of shallow faulting. We apply a multi-trace similarity technique to identify discontinuities in the seismic data that may be attributed to faults and fractures. This fault detection approach reveals diverse fault damage patterns on adjacent seismic profiles. However, a discernible damage zone pattern emerges by stacking multiple damage detection profiles along strike. We find that peak damage identified in this way corresponds to the active main fault strand, confirmed in this study, and thus the technique may be useful for identifying active fault strands elsewhere. Additionally, we observe that the variable width of the damage zone along strike is controlled by fault obliquity. Furthermore, our observations reveal a correlation between fault damage and seafloor fluid seeps visible in the water column, suggesting that damage plays a role in controlling fluid flow around the fault.

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USGS2024

An evaluation of tradeoffs in restoring ephemeral vs. perennial habitats to conserve animal populations

Introduction: Habitat loss and degradation pose significant threats to global fish and wildlife populations, prompting substantial investments in habitat creation and restoration efforts. Not all habitats provide equal benefits, leading to challenges in prioritizing restoration actions. For example, juvenile anadromous salmonids require high quality rearing aquatic habitats to achieve the physiological requirements needed to successfully migrate to the ocean. However, there are profound disagreements among anadromous salmon restoration managers whether it is best to focus efforts on restoring in-channel habitats that are available for the entire rearing period or floodplain habitats that, while facilitating greater growth and survival than in-channel habitats, are only available for a few weeks at a time and are typically only activated every two-to-three years. Methods: We used an existing fall-run Chinook salmon decision-support model to evaluate under what conditions floodplain restoration would provide greater benefits than in-channel habitat restoration. The simulations included a wide range of floodplain inundation frequencies and durations and floodplain benefits in the form of increased survival and growth relative to in-channel habitats. Results: The simulations results indicated that in-channel habitat restoration was always the best habitat restoration action when there was no existing in-channel habitat despite simulating a wide range of flood frequency, duration, and growth and survival benefits. Floodplain restoration was generally best when there was sufficient in-channel habitat available to successfully rear most of the juveniles produced by the returning adult salmon. Discussion: We hypothesize that in-channel and floodplain habitats have different roles in salmon population maintenance with in-channel habitats regulating the overall population size and floodplains acting as recurrent resource pulses. Our study provides a quantitative framework to evaluate the benefit of these two habitat types and provides generalizable rulesets that can be used by managers when implementing habitat restoration strategies for species that inhabit both in-channel and floodplain habitats.

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USGS2024

The 17 January 1994 Northridge, California, earthquake: A retrospective analysis

The 17 January 1994 Northridge, California, earthquake was a watershed event, with far-reaching societal and scientific impacts. The earthquake, which occurred in the early days of both broadband seismic networks and the Internet, spurred advances in seismic monitoring, real-time systems, and development of data products. Motivated by the 30th anniversary of the earthquake, we present a brief retrospective of the earthquake and its impact, and reconsider both ground motions and the aftershock distribution using modern tools and best-available data. With improvements in instrumentation and analysis methodology, recent earthquakes continue to reveal increasing complexity of ground motions, fault systems, and earthquake ruptures. Even in the absence of data from state-of-the art instrumentation, a retrospective consideration of ground motion data from the Northridge earthquake reveals complexities beyond what could be characterized (and modeled) thirty years ago. Aftershock relocations for both the 1971 Sylmar and 1994 Northridge earthquakes also reveal an updated view of fault complexity. Our study does provide a cautionary tale regarding legacy data sets and research results that are not easily accessible, which can result in discrepancies between catalog data and products from best-available science. We also briefly describe outreach products produced as part of the anniversary commemoration.

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USGS2024

Estimating biogeochemical rates using a computationally efficient Lagrangian approach

Nutrient concentrations in many estuaries have increased over the past century due to increases in wastewater discharge and increased agricultural intensity, contributing to multiple environmental problems. Numerous biogeochemical and physical processes in estuaries influence nutrient concentrations during transport, resulting in complex spatial and temporal variability and challenges identifying predominant processes and their rates. Mechanistic models which require these rates to quantify biogeochemical processes become complex and difficult to calibrate as the number of processes and parameters grows, owing to the high dimensionality of the parameter space and the computational cost of simultaneously modeling the transport and transformations of constituents. We developed a modeling approach that decouples transport from transformations, enabling fast, data-driven exploration of the parameter space. The approach extracted information including water age, cumulative exposure to specific habitats, and mean water depth exposure from a hydrodynamic model. Using this information, a biogeochemical model was implemented to predict ammonium and nitrate concentrations in a Lagrangian frame. The model performed each simulation in milliseconds on a laptop computer, allowing the fitting of rate parameters for key transformations by optimization. The optimization used fixed station nitrate observations and the model was then validated against high-resolution mapping observations of ammonium and nitrate. The results suggest that the observed spatial and temporal variation can be largely represented with five transformation processes and their associated rates. Dissolved inorganic nitrogen (DIN) losses occurred only in shallow vegetated areas in the model, highlighting that biogeochemical processes in these areas should be included in DIN models.

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USGS2024

Wetland seed abundance estimates influenced by soil core volume

Soil core sampling is commonly used to estimate moist-soil seed abundance when assessing waterfowl habitat and population carrying capacity. Several studies have evaluated the limitations and sources of bias associated with soil core sampling, but few have examined how variable sample volumes can influence estimates of seed abundance. We measured the soil volume of 1,128 soil cores collected from managed seasonal wetlands and tidal marshes to determine if seed abundance was correlated with the volume of soil sampled. We collected soil cores using a standard (6 cm diameter, 5 cm deep) soil coring device with external flanges to control sampling depth. We found that the actual soil volume sampled was highly variable (45 ml to 560 ml). Mean soil volume (215.6 ml) was 53% greater than the targeted soil volume based on the dimensions of the coring device (141.4 ml). Moreover, total seed mass was positively correlated with soil volume sampled in managed wetlands but not in tidal marshes. Using a linear model, we found managed wetland samples contained an additional 33.2 kg/ha of total seeds due to the extra 74.2 ml of soil collected per sample on average. Total seed abundance in managed wetlands was estimated to be 19.6% greater due to the oversampling of soil. Estimates of seed abundance in moist-soil wetlands derived from soil core samples may be improved by considering the variability in the actual soil core volumes sampled using standard sampling tools.

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USGS2024

Distribution, Abundance, and Breeding Activities of the Southwestern Willow Flycatcher at Marine Corps Base Camp Pendleton, California—2020 Annual Report

Executive Summary Surveys for the endangered Southwestern Willow Flycatcher ( Empidonax traillii extimus ) were done at Marine Corps Base Camp Pendleton (MCBCP or “Base”), California, between May 4 and July 31, 2020. All of MCBCP’s historically occupied riparian habitat (core survey area) was surveyed for flycatchers in 2020. Additionally, one-fifth of the unoccupied riparian habitat (non-core survey area) was surveyed for flycatchers. Thirteen transient Willow Flycatchers of unknown subspecies were observed on four of the seven drainages surveyed in 2020. No Willow Flycatchers were detected at Fallbrook Creek, Pilgrim Creek, or San Mateo Creek. Transients occurred in a range of habitat types, including mixed willow ( Salix spp.) riparian, riparian scrub, willow-sycamore ( Platanus racemosa ) or willow-cottonwood ( Populus fremontii ) dominated riparian vegetation, and upland scrub. Exotic vegetation, primarily poison hemlock ( Conium maculatum ), was present in most flycatcher locations. The resident population of Southwestern Willow Flycatchers on MCBCP declined 33 percent from three individuals in 2019 to two individuals in 2020. In 2020, the resident Southwestern Willow Flycatcher population on Base consisted of one male and one female. No single males or non-territorial floaters were observed in 2020. Overall, one territory was established consisting of one monogamous pair. Resident flycatchers were restricted to the Santa Margarita River, and distribution was limited to the Pueblitos breeding area. All resident flycatchers were located in mixed willow riparian habitat. Nesting was initiated in late May and continued into early August. Three nesting attempts were documented, of which 33 percent (1/3) were successful. Predation and substrate failure accounted for the two nest failures. Two fledglings were produced, yielding a seasonal productivity of two young/pair. No instances of Brown-headed Cowbird ( Molothrus ater ) parasitism were observed. Flycatchers placed nests in two plant species: native sandbar willow ( Salix exigua ) and exotic poison hemlock. One hundred percent of resident birds that were present at MCBCP in 2020 were banded in previous years; no unbanded birds were detected. Of the three uniquely banded adult flycatchers present during the 2019 breeding season, 100 percent (1/1) of males and 50 percent (1/2) of females returned to MCBCP in 2020, and both banded flycatchers returned to the same breeding area they occupied in 2019. None of the seven nestlings banded in 2019 returned to MCBCP in 2020, and none were detected off Base. Six nestlings from two nests were banded in 2020; only two survived to fledging. From 2000 to 2020, overall adult survival of Southwestern Willow Flycatchers on MCBCP was 60 percent, while first-year survival was 20 percent. A conspecific attraction study initiated on Base in 2018 and repeated annually through 2020 found that 100 percent of breeding flycatchers detected in 2020 settled close to automated playback units.

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USGS2024

Distribution, abundance, and breeding activities of the Least Bell's Vireo at Marine Corps Base Camp Pendleton, California—2020 annual report

Executive Summary The purpose of this report is to provide the Marine Corps with an annual summary of abundance, breeding activity, demography, and habitat use of endangered Least Bell’s Vireos ( Vireo bellii pusillus ) at Marine Corps Base Camp Pendleton (MCBCP, or Base). Surveys for the Least Bell's Vireo were conducted at MCBCP, California, between April 1 and July 10, 2020. Core survey areas and a subset of non-core areas in drainages containing riparian habitat suitable for vireos were surveyed 3–4 times. We detected 669 territorial male vireos and 16 transient vireos in core survey areas. An additional 156 territorial male vireos were detected in non-core survey areas. Territorial vireos were detected on all 10 drainages/sites surveyed (core and non-core areas). Of the vireo territories in core areas, 88 percent were on the 4 most populated drainages, with the Santa Margarita River containing 69 percent of all territories. In core areas, 79 percent of male vireos were confirmed as paired; 83 percent of male vireos in non-core areas were confirmed as paired. The number of documented Least Bell’s Vireo territories in core survey areas on MCBCP (669) increased 39 percent from 2019 to 2020. The number of territories in all core survey area drainages increased by one or more between 2019 and 2020. The substantial increase in vireo numbers on MCBCP (39 percent) was consistent with population changes in surrounding areas, including the lower San Luis Rey River (26 percent), Marine Corps Air Station, Camp Pendleton (58 percent), and the middle San Luis Rey River (7 percent). Most core-area vireo territories (69 percent of males) occurred in willow ( Salix spp.) riparian habitat. An additional 4 percent of birds occupied willow habitat co-dominated by Western sycamores ( Platanus racemosa ) or Fremont cottonwoods ( Populus fremontii ). Eighteen percent of territories were found in riparian scrub dominated by mule fat ( Baccharis salicifolia ) or sandbar willow ( S. exigua ). Upland scrub was used by 7 percent or fewer vireos; 1 percent of territories occurred in non-native vegetation, and less than 1 percent of vireo territories occurred in habitat co-dominated by coast live oak ( Quercus agrifolia ) and sycamore. In 2019, MCBCP began operating an artificial seep along the Santa Margarita River. The artificial seep pumped water to the surface from March through August each year during daylight hours and was designed to increase the amount of surface water present to enhance Southwestern Willow Flycatcher ( Empidonax traillii extimus ; flycatcher) breeding habitat. Although this enhancement was designed to benefit flycatchers, few flycatchers have inhabited the seep and proposed seep areas within the past several years. Therefore, vireos were selected as a surrogate species to determine effects of the habitat enhancement. This report presents preliminary analyses of vireo and vegetation response to the existing artificial seep. We sampled vegetation in the Seep site and three Reference sites to determine the effects of a new water diversion dam that was completed in 2019 and a surface water enhancement seep pump installed along the Santa Margarita River. We found minor differences in non-native vegetation cover between Reference sites and the Seep site. However, soil moisture was higher at the Reference sites compared to the Seep site. The effect of the seep pump may have been masked by high precipitation in the bio-year (July 1‒June 30) before 2020, limited time for the water diversion to have an effect, well-draining soil, and the non-operation of two to three of the six seep outlets. We color banded and resighted color banded Least Bell’s Vireos to evaluate adult site fidelity, between-year movement, and the effect of surface water enhancement on vireo site fidelity and between-year movement. We banded 146 Least Bell's Vireos for the first time during the 2020 season. Birds banded included 27 adult vireos and 119 juvenile vireos. All adult vireos were banded with unique color combinations. The juvenile vireos (all nestlings) were banded with a single gold numbered federal band on the left leg. We resighted and identified 85 Least Bell's Vireos banded before the 2020 breeding season on Base in 2020. Of the 85, 13 vireos were originally banded on the San Luis Rey River, 2 were banded in Baja California Sur, 1 was banded at Marine Corps Air Station, Camp Pendleton, and the remaining birds were banded at MCBCP. Adult birds of known age ranged from 1 to 8 years old. Most returning adult vireos showed strong between-year site fidelity. Of the adults present in 2019 and 2020, 74 percent, (79 percent of males; 40 percent of females) returned to within 100 m of their previous territory. The average between-year movement for returning adult vireos was 0.3 plus or minus (±) 0.8 kilometer (km). The average movement of first-year vireos detected in 2020 that fledged from a known nest on MCBCP in 2019 was 4.7±7.0 km. One first-year vireo that originated at MCBCP moved off Base and was detected at Murrieta Creek, 23.0 km from his natal territory. We monitored Least Bell's Vireo pairs to evaluate the effects of surface water enhancement on nest success and breeding productivity. Vireos were monitored at one Seep site and three Reference sites. Base personnel plan to install a second seep pump at one of the Reference sites in the future, at which time the status of the monitoring site will change from Reference to Seep. Nesting activity was monitored between March 31 and July 28 in 52 territories within the Seep and Reference sites (12 at the Seep site and 40 at Reference sites). All territories were occupied by pairs, and all but one territory was fully monitored, meaning all nesting attempts were monitored at these territories. One vireo territory within a Reference site was partially monitored. During the monitoring period, 94 nests (25 in the Seep site and 69 in Reference sites) were monitored. Breeding productivity was similar at the Seep site and Reference sites (3.7 and 2.9 young per pair, respectively), with 75 percent of Seep pairs and 79 percent of Reference pairs successfully fledging at least 1 young in 2020. Compared to Reference sites, the Seep site had a higher proportion of all eggs that hatched and also a higher proportion of nests with eggs that hatched. Conversely, a lower proportion of hatchlings and nests that had hatchlings fledged at the Seep site than at Reference sites. According to the best model, nest survival in 2020 was not affected by treatment (Seep versus Reference), although the second best model that included treatment was also well supported. Completed nests at the Seep site were likely to be as successful as nests at Reference sites in 2020 (57 percent and 59 percent, respectively). Predation was believed to be the primary source of nest failure at both sites. Predation accounted for 90 percent and 73 percent of nest failures at Seep and Reference sites, respectively. Failure of the remaining eight nests was attributed to the collapse of the nesting substrate, exposure to rain and flooding, and other unknown reasons. Fourteen plant species were used as hosts for vireo nests in 2020. In 2020, we found that at the Seep site, successful nests were placed in taller host plants and further from the edge of host plants (closer to the center) than unsuccessful nests. We found no difference in nest placement between the Seep site and the Reference sites.

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USGS2024

Evaluation of extinction risk for stream fishes within an urban riverscape using population viability analysis

1. The Santa Ana River in the Los Angeles region of California demonstrates common habitat degradation symptoms that are characteristic of the urban stream syndrome. These impacts have altered the Santa Ana River community structure, with few species as impacted as the native Santa Ana sucker (sucker; Pantosteus santaanae ). 2. Consequently, a recovery plan developed for sucker identified the need for a population viability analysis (PVA) to assess sucker extirpation risk. However, PVAs can be data-intensive and are subject to several sources of bias when standardized protocols are absent. 3. More than 20 years of sucker and arroyo chub (chub; Gila orcuttii ) surveys using different methods were compiled to build an integrated hierarchical multi-population PVA to estimate trends in abundance and extirpation probability of these native fishes from the Santa Ana River. 4. PVA modelling indicated similar patterns in sucker and chub abundance along the Santa Ana River, with the highest abundance of both species in the upper regions of the river during the early 2000s and downstream in recent years (2018–2022). Extirpation risk was estimated to be greatest near wastewater treatment facilities, where native fish abundance estimates have been zero since 2018. Extirpation risk was lower downstream of the wastewater treatment facilities for both species, although extinction risk was higher for sucker than chub throughout the river. 5. As the model evolves and more data are collected, the PVA could be used to assess the effects of various management actions, such as non-native predator removals and native fish re-introductions, on sucker and chub persistence.

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USGS2024

The Ojai California earthquake of 20 August 2023: Earthquake early warning performance and alert recipient response in the Mw 5.1 event

A magnitude 5.1 earthquake in California rarely generates more than momentary notice—a headline in local newspapers and a mention with footage on the evening news—then fades into obscurity for most people. But this earthquake, which occurred near the city of Ojai, is important for seismologists, social scientists, emergency managers, policymakers, and others who are engaged in implementing and improving earthquake early warning (EEW) technology and in assessing its value in public warnings. In this earthquake, ShakeAlert, the EEW system for the West Coast of the United States operated by the U.S. Geological Survey (USGS), was publicly activated and, for the first time, a substantial number of those who received alerts provided feedback on various aspects of the alerts they received. To capture data related to public attitudes and assessments regarding this and future alerts, a supplemental questionnaire was developed and associated with the “Did You Feel It?” (DYFI) earthquake reporting system, also operated by the USGS. The DYFI system received over 14,000 felt reports; 2490 of these were by people who received or expected to receive an alert before the onset of earthquake motion at their locations. This article analyzes the aggregate results of these EEW user reports, touching on the respondent’s situation upon receiving the alert, characteristics of the alert received, and, perhaps, most importantly, how the alert recipient responded if received before feeling earthquake motion. The new DYFI EEW supplemental questionnaire also inquired about respondent views of alert usefulness and preferences in future alerts. Our report provides a first glimpse of a range of behaviors, attitudes, and assessments by users of the recently implemented EEW system for the U.S. West Coast.

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USGS2024

Distribution, abundance, and habitat characteristics of Coastal Cactus Wrens (Campylorhynchus brunneicapillus) in San Diego County, California—2023 Data Summary

Executive Summary We surveyed for coastal Cactus Wren ( Campylorhynchus brunneicapillus ) in 507 established plots in San Diego County in 2023, encompassing 4 genetic clusters (Otay, Lake Jennings, Sweetwater/Encanto, and San Pasqual). Two surveys were completed at each plot between March 1 and July 31. Cactus Wrens were detected in 181 plots (36 percent of plots). Cactus Wrens were detected in 26 percent of plots that have been consistently surveyed since 2020, indicating lower plot occupancy than in 2022 (31 percent), 2021 (34 percent), and 2020 (35 percent). There were 158 Cactus Wren territories detected across all survey plots in 2023. In plots that have been consistently surveyed since 2020, we documented 85 territories, which is a decrease from 94 territories in 2022, 113 territories in 2021, and 109 territories in 2020. The number of territories declined from 2022 to 2023 in the Lake Jennings, Sweetwater/Encanto, and San Pasqual genetic clusters but remained virtually the same in the Otay genetic cluster. At least 80 percent of Cactus Wren territories were occupied by pairs, and 125 fledglings were observed in 2023. We observed 14 banded Cactus Wrens in 2023, 9 of which we could identify individually by color band combination. Adults of known age ranged from 4 to 7 years old. All individually identifiable adult Cactus Wrens occupied the same territory in 2023 that they occupied in 2022, and we detected no movement of banded Cactus Wrens between genetic clusters. Vegetation at Cactus Wren survey plots was dominated by coastal sage scrub shrubs, such as California sagebrush ( Artemisia californica ), California buckwheat ( Eriogonum fasciculatum ), lemonade berry ( Rhus integrifolia ), jojoba ( Simmondsia chinensis ), and San Diego viguiera ( Bahiopsis laciniata ). No definitive signs of fungal pathogens were observed on cactus within and around survey plots. Blue elderberry ( Sambucus mexicana ) was detected at 41 percent of plots, and Cactus Wrens occupied proportionally more plots with elderberry than plots without elderberry. Very little dead or unhealthy cactus was observed within all survey plots, and Cactus Wren occupancy did not differ between plots with high or low amounts of dead or unhealthy cactus. Almost 90 percent of plots had more than 5 percent of cactus crowded or overtopped by vines and shrubs, and Cactus Wren occupancy did not differ between plots with high or low amounts of cactus crowded or overtopped by vines and shrubs. Non-native annual cover was more prevalent in survey plots in 2023 than in 2022. Cactus Wrens did not select or avoid plots with more non-native cover.

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USGS2024

Relatively stable pressure effects and time-increasing thermal contraction control Heber geothermal field deformation

Due to geological complexities and observational gaps, it is challenging to identify the governing physical processes of geothermal field deformation including ground subsidence and earthquakes. In the west and east regions of the Heber Geothermal Field (HGF), decade-long subsidence was occurring despite injection of heat-depleted brines, along with transient reversals between uplift and subsidence. These observed phenomena contradict current knowledge that injection leads to surface uplift. Here we show that high-yield production wells at the HGF center siphon fluid from surrounding regions, which can cause subsidence at low-rate injection locations. Moreover, the thermal contraction effect by cooling increases with time and eventually overwhelms the pressure effects of pressure fluctuation and poroelastic responses, which keep relatively stable during geothermal operations. The observed subsidence anomalies result from the siphoning effect and thermal contraction. We further demonstrate that thermal contraction dominates long-term trends of surface displacement and seismicity growth, while pressure effects drive near-instantaneous changes.

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USGS2024

Conservation genetics of the endangered California Freshwater Shrimp (Syncaris pacifica): Watershed and stream networks define gene pool boundaries

Understanding genetic structure and diversity among remnant populations of rare species can inform conservation and recovery actions. We used a population genetic framework to spatially delineate gene pools and estimate gene flow and effective population sizes for the endangered California Freshwater Shrimp Syncaris pacifica . Tissues of 101 individuals were collected from 11 sites in 5 watersheds, using non-lethal tissue sampling. Single Nucleotide Polymorphism markers were developed de novo using ddRAD-seq methods, resulting in 433 unlinked loci scored with high confidence and low missing data. We found evidence for strong genetic structure across the species range. Two hierarchical levels of significant differentiation were observed: (i) five clusters (regional gene pools, F ST = 0.38–0.75) isolated by low gene flow were associated with watershed limits and (ii) modest local structure among tributaries within a watershed that are not connected through direct downstream flow (local gene pools, F ST = 0.06–0.10). Sampling sites connected with direct upstream-to-downstream water flow were not differentiated. Our analyses suggest that regional watersheds are isolated from one another, with very limited (possibly no) gene flow over recent generations. This isolation is paired with small effective population sizes across regional gene pools (N e = 62.4–147.1). Genetic diversity was variable across sites and watersheds ( H e = 0.09–0.22). Those with the highest diversity may have been refugia and are now potential sources of genetic diversity for other populations. These findings highlight which portions of the species range may be most vulnerable to future habitat fragmentation and provide management consideration for maintaining local effective population sizes and genetic connectivity.

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