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At least 37 records · Page 2Linked to original sources

USGS2026

A strategic method for expanding the Pacific Flyway Motus network

Understanding the movement and survival of birds of conservation concern during migration is critical for guiding conservation action. Unfortunately, the migratory life stage is understudied in many bird species because of the challenges of following such species over large distances, particularly those with small body sizes. One established method for tracking movement of small avian species is the Motus Wildlife Tracking System. This international collaborative network provides a powerful tool for tracking survival and movement, enabling estimation of parameters such as stopover duration, migratory connectivity, dispersal, and survival that are otherwise difficult to measure. While the Motus network is well established in eastern North America, coverage in the western part of the continent is limited, constraining sample sizes needed for robust demographic modeling. Expanding the Motus network is therefore a high priority for Pacific Flyway agencies. To date, methods for determining priority locations for new Motus receiving stations do not explicitly incorporate species occurrence. In collaboration with partners across the western United States and the Canadian Province of British Columbia, we used eBird data to prioritize strategic locations for new Motus receiving stations. We modeled multi-species co-occurrence, defined by abundance thresholds met in multiple weeks, using environmental and survey covariates while accounting for imperfect detection. Using occupancy model predictions, we identify high-use areas where new Motus stations are most likely to detect multiple species of interest. While the predictive maps provide a framework for strategically expanding the Motus network and supporting conservation of migratory stopover and wintering habitats in the Pacific Flyway, we also provide the analysis code and prediction output to support the expansion of Motus in additional regions.

Pacific flyway↗

USGS2026

Geophysical insights into Kīlauea’s eruptive reawakening after its 2018 eruption and caldera collapse

A little more than two years after the destructive 2018 lower East Rift Zone eruption and summit collapse ended, renewed volcanic activity began at Kīlauea volcano, Hawaiʻi. During 2020–2025, activity at the volcano included six eruptions in the summit caldera, one in the Southwest Rift Zone, and one in the middle East Rift Zone, as well as multiple non-eruptive intrusions in all three locations. We categorize the volcano’s activity post-2018 into four phases based on eruption locations and style, as well as patterns of magma storage and migration inferred from geophysical data. In some cases, these observations illuminated parts of the volcano’s magmatic system for the first time since the advent of modern geophysical monitoring—particularly deformation datasets that include tilt, continuous GNSS, and InSAR. Analyses of these geodetic data and complementary seismic, geological, and geochemical observations provide an opportunity to explore summit and rift zone connectivity, rift-zone magma storage conditions, the variable geophysical manifestations of eruption onsets, magma-fault interactions, and other long-standing questions associated with eruptions and intrusions at Kīlauea.

Hawaii↗

USGS2026

Assessment of Undiscovered Conventional Gas Resources in the Northern Alaska Province, 2026

Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean conventional resources of 96 trillion cubic feet of gas in the Northern Alaska Province.

Fact Sheet↗

USGS2026

Genetic bottleneck and panmixia following the collapse of a Great Lakes lake whitefish fishery

Lake whitefish Coregonus clupeaformis abundance has declined throughout most of the Laurentian Great Lakes in North America for two decades. Current management strategies in Lake Erie assume that there is a single stock of lake whitefish that spawns in the West Basin. There is documented lake whitefish spawning activity throughout the lake, leading to questions about locally adapted genetic stocks. Past research on lake whitefish genetic structure in Lake Erie has supported the single-stock hypothesis, but these studies used only neutral genetic markers or contained a limited number of samples that were collected during the spawning season when stocks would be spatially isolated. Using a GT-seq panel, we evaluate the genetic structure of lake whitefish collected from spawning shoals in the West, Central, and East basins of Lake Erie and compare these populations to lake whitefish from Lake Huron. We then investigate evidence of local adaptation and conduct demographic reconstruction using whole-genome sequencing. Our goals were to conclusively quantify intra-lake genetic structure in Lake Erie and determine whether spawning aggregations possess putatively adaptive variants that could be used for genetic stock identification at a sub-lake level. Our analysis supported the single-stock hypothesis in Lake Erie. However, Lake Erie stocks were distinct from neighboring Lake Huron. Whole-genome analysis did not identify any strong evidence of adaptive loci differentiating stocks. Inference of historic effective population size suggests that declines in lake whitefish populations may have caused a genetic bottleneck. Combined, these results indicate that lake whitefish in Lake Erie may have experienced an Allee Effect after population declines, resulting in a loss of population structure and genetic diversity as spawning shoals were recolonized from a common source.

Michigan, Ohio, Ontario↗

USGS2026

ECCOE Landsat quarterly calibration and validation report—Quarter 2, 2026

Open-File Report↗

USGS2026

From sediment pulse to ecological recovery: A nine-year study of benthic macroinvertebrate response to Elwha River dam removal

Large dam removals are increasingly important river restoration actions, but long-term ecological responses remain poorly understood, especially for removals involving large sediment releases. We evaluated benthic macroinvertebrate (BMI) responses following removal of the Elwha and Glines Canyon dams on the Elwha River, Washington, USA. At the time of removal (2011–2014), these were the largest dams to be dismantled worldwide. Dam removal reconnected over 90% of the watershed to anadromous fish, released more than 20 megatonnes of reservoir sediment downstream, and restored natural sediment and wood transport processes. Using nine years of monitoring data spanning periods before, during, and after dam removal, we quantified changes in BMI density, taxa richness, and community composition across five river sections exposed to different combinations of sediment disturbance, reservoir succession, and fish reintroduction. Sediment release substantially altered downstream physical habitat and was accompanied by pronounced declines in BMI density and richness, particularly downstream of both dams. Density declined by up to 95% during active dam removal but rebounded to near baseline levels within three years after peak sediment transport subsided. In contrast, taxa richness and community composition remained significantly altered three years after dam removal, with persistent reductions particularly evident among Trichoptera and long-lived taxa. Fine sediment was the environmental variable most strongly associated with changes in BMI community structure. Our results demonstrate that large dam removal can cause severe but largely transient reductions in BMI abundance while producing longer-lasting changes in taxonomic diversity and community composition. These findings highlight the importance of distinguishing between numerical and ecological recovery and suggest that recovery trajectories following large dam removal extend well beyond the period of active sediment release.

Washington↗

USGS2026

ECCOE Landsat quarterly calibration and validation report—Quarter 1, 2026

Executive Summary The U.S. Geological Survey Earth Resources Observation and Science Calibration and Validation (Cal/Val) Center of Excellence (ECCOE) focuses on improving the accuracy, precision, calibration, and product quality of remote-sensing data, leveraging years of multiscale optical system geometric and radiometric calibration and characterization experience. The ECCOE Landsat Cal/Val Team continually monitors the geometric and radiometric performance of active Landsat missions and makes calibration adjustments, as needed, to maintain data quality at the highest level. This report provides observed geometric and radiometric analysis results for Landsats 8 and 9 for quarter 1 (January–March) of 2026. All data used to compile the Cal/Val analysis results presented in this report are freely available from the U.S. Geological Survey EarthExplorer website: https://earthexplorer.usgs.gov . One specific activity that the ECCOE Landsat Cal/Val Team closely monitored was a Landsat 8 Thermal Infrared Sensor encoder alerts anomaly. On March 18, 2026, the Thermal Infrared Sensor instrument’s mechanism control electronics board reset, driving several parameters to default power-on values. Subsequent telemetry and analysis determined that no persistent hardware misconfiguration was present and no radiometric or geometric degradation was observed.

Open-File Report↗

USGS2026

Highly pathogenic H5N1 avian influenza infection and exposure in waterfowl and waterbirds of the Sacramento National Wildlife Refuge Complex, 2022-2025

The introduction of clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 into North America in 2021 marked a significant shift in disease dynamics for wild waterfowl populations. To assess infection and seroprevalence trends following this incursion, we leveraged ongoing capture efforts at the Sacramento National Wildlife Refuge Complex between October 2022 and July 2025 to conduct sampling for HPAI H5N1 prevalence and seroprevalence. Our efforts resulted in the analysis of 384 swab and 204 sera samples from assorted waterfowl and waterbird species. HPAI H5N1 infection was confirmed in only three individuals (two Snow Geese and one Greater White-fronted Goose), all asymptomatic at capture. Antibodies to influenza A viruses (IAVs) were detected in all duck and goose species with the majority of positive samples also testing positive for antibodies to both H5 and N1, demonstrating a relatively high population level of previous exposure and likely immunity that aligns with previous findings in these species. This study also reports the first known observation of H5 antibodies in American Coot, though both overall IAV seroprevalence and H5 specific antibodies were notably lower than in sympatric waterfowl. This disparity suggests that American Coot may have lower susceptibility to infection or exhibit behavior that limits exposure compared to sympatric waterfowl. Together these results underscore the value of serologic surveillance as a supportive surveillance strategy to better inform potential management strategies related to HPAI H5N1 risk in wild birds.

California↗

USGS2026

Erupted volume during the 2014–2023 Semisopochnoi unrest and eruption constrained by multi-platform InSAR and volcanic gas observations

Volcano deformation data provide important constraints on magma dynamics during volcanic unrest and eruptions. From these observations, we can estimate subsurface pressure changes and relate them to volume change in the reservoir. However, because magma and rock are compressible, this volume change cannot be directly equated with eruptive volume. When we combine geodetic analyses with gas observations, petrologic constraints, volatile solubility modeling, and magma compressibility equations, however, we can estimate realistic lower and upper bounds of eruptive volume. Leveraging multi‐platform InSAR time series and satellite SO 2 data, we apply these methods to the 2014–2023 unrest and eruption of Semisopochnoi, Alaska. We find that this phreatomagmatic eruption sequence was fed by a spherical magma source at 6.5–7.5 km depth bsl, centered beneath the caldera, ∼5 km offset to the east from the vent. Volatile solubility modeling indicates that ∼50% of the initial dissolved CO 2 has exsolved at depths consistent with the geodetic source depth, increasing the magma compressibility. Combining geodetic model constraints with SO 2 observations, petrologic constraints, solubility models, and magma compressibility findings yields 12–32 Mm 3 as the most‐likely juvenile, dense‐rock equivalent eruptive volume, with a best estimate of 20 Mm 3 . Stress change modeling suggests that the local stress field encouraged conduit formation west of the pre‐eruptive inflation center, and that the 2014 M7.9 Rat Island earthquake, ∼65 km to the west of Semisopochnoi, reduced the compressive stress underneath the volcano, supporting prolonged eruptive activity.

Alaska↗

USGS2026

Atlas of pollen and spores from forests and wetlands in the mid-Atlantic Coastal Plain, USA

This atlas includes descriptions and illustrations of pollen and spores from plant species found in the mid-Atlantic Coastal Plain of the United States of America, with a focus on taxa that grow in or near riparian wetlands. We include light micrographs and detailed descriptions of 141 species spanning 106 genera and 69 families. This atlas was compiled to facilitate the identification of palynomorphs from sedimentary archives in the mid-Atlantic region. We include both wetland taxa and those from surrounding uplands that may be deposited in wetland sediments.

North Carolina, South Carolina, Virginia↗

USGS2026

Exploring future ecogeomorphic state transitions of an undeveloped barrier island: Multidecadal model projections for North Core Banks, NC, USA

Ecogeomorphic state transitions in coastal barrier systems will be impacted and likely amplified by projected accelerated sea-level rise and enhanced storm intensity over the next several decades. When, where, and how these transitions will take place remain uncertain and complex, yet are of primary interest to coastal managers looking to prepare for future changes. Here, we apply the new Mesoscale Explicit Ecogeomorphic Barrier model to generate probabilistic projections of future ecogeomorphic state transitions up to year 2050 for the undeveloped North Core Banks (NCB), North Carolina, United States. In our full probabilistic projection, which accounts for stochasticity from uncertainty in sea-level rise and high-water event (HWE) projections, loss of barrier interior to passive sea-level rise submergence dominates ecogeomorphic state transitions, suggesting that the biggest threat to many undeveloped barriers in the next several decades will come from the back-barrier rather than ocean-side. Additionally, this projection suggests that dune and unvegetated interior states are most volatile, with the intensity of state transitions varying significantly alongshore. In projections simulating a range of deterministic sea-level rise rates, higher rates enhance: overwash frequency; loss of beach and dune states; and interior submergence. We also find that state transitions are less sensitive to HWE intensity than sea-level rise, and that more frequent, moderate HWEs—rather than the largest events—may be the principal drivers of mesoscale ecogeomorphic state change. Our projections highlight important future mesoscale trends of ecogeomorphic state transitions for NCB that are likely relevant to other stable, sediment-rich barrier systems of U.S. coastlines.

North Carolina↗

USGS2026

Big data for small streams: Leveraging a coarse national model to enhance fine-resolution stream temperature predictions

Predictive stream temperature models are commonly used to address spatial and temporal gaps in observational data because stream temperature information is essential for environmental management decisions. National models capture broad patterns driven by climate, topography, and seasonality, but often lack the spatial resolution to simulate fine-scale variation in groundwater discharge, riparian shading, or tributary inflows. In contrast, watershed models may simulate finer-resolution patterns but miss regional drivers or be limited by scarcity of observations. To generate watershed-extent, fine-resolution stream temperature predictions, we developed 18 multiscale machine-learning models that leverage (a) a broad-extent, coarse-resolution stream temperature model and (b) finer-resolution observations and predictor data. The coarse-resolution model simulates daily stream temperature across the conterminous United States on the National Hydrologic Geospatial Fabric (13.7 km median reach length; 865,364 km total). The fine-resolution models simulate daily stream temperature on the National Hydrography Dataset Plus version 2 (1.5 km median; 5,192,808 km total). We compared multiscale models to seven purely broad- (national) or watershed-extent models, testing them in eight watersheds (436–985 km 2 ) with differing hydrologic settings and under realistic data availability scenarios. Especially when observations within a watershed were scarce, multiscale models generated more accurate predictions than national or watershed-specific models. A recurrent graph convolution neural network pretrained on coarse predictions and fine-tuned on watershed-specific observations was most accurate across watersheds and data scenarios. These results highlight that leveraging both coarse, national results and watershed-specific data can increase model accuracies, particularly when observations within a watershed are spatially or temporally limited.

Water Resources Research↗

USGS2026

The flip side of destructive wildfires: A water supply buffer to climate change

Wet to dry climate extremes in California have directly or indirectly impacted droughts, wildfires, and floods, resulting in costly damage. Reservoirs in California were built to store snowpack into the summer and provide multiple benefits in the state: they offer municipal and agricultural water resources during the dry season and prevent flooding downstream. The upper Feather River watershed, which drains 9300 square kilometers (km 2 ) into Lake Oroville, provides water to over 27 million people and 3000 km 2 of farmland. The North Complex Fire in 2020 and the Dixie and Sugar Fires in 2021 burned over 50% of the watershed, and their long-term impact on the upper Feather River water supply was previously unknown. This study quantified post-wildfire (postfire) changes in plant water use, soil moisture, and streamflow due to changes in vegetation using a physically based water balance model. Long-term trends revealed decreases in annual precipitation and mid- to high-elevation snowpack in this watershed from 1981 to 2020. Due to changes in vegetation, annual postfire streamflow at Feather River at Oroville increased by 22%, 32%, and 16% while summer baseflows increased by 5%, 12%, and 2% in water years (WYs) 2022 through 2024, respectively. Larger increases in streamflow occurred during WY 2023, an extremely wet year relative to the other years, highlighting the challenges in quantifying and managing hydrologic systems with naturally high interannual variability. Seasonal soil moisture increased by up to 34% depending on the location, predominantly in fall and summer postfire. Despite observed historical decreases in precipitation and snowpack, changes in vegetation due to wildfires or other disturbances may increase water availability, and continued management of mixed-conifer forests (i.e. thinning and controlled burns) may help offset future reduced precipitation and snowpack and therefore increase water supply resilience.

Callfiornia↗

USGS2026

MusselFinder: Automated dreissenid mussel density estimation via robotic benthic imaging

Despite the widespread need to map the abundance of invasive quagga and zebr mussels ( Dreissena spp.) in lakes and reservoirs worldwide, current methods remain limited by data collection and analysis bottlenecks. Autonomous underwater vehicles (AUVs) combined with machine learning (ML) offer a scalable remote sensing approach for estimating mussel density (individuals m −2 ) across large spatial domains and a range of habitats that are difficult to sample with current techniques. We present MusselFinder: a deep neural network (DNN)-based pipeline that detects and enumerates live mussels in AUV-collected benthic images. MusselFinder estimates live mussel percent cover and density in nadir monocular images captured at known altitudes above the lakebed. In images of suitable clarity, MusselFinder achieved strong pixel-level localization (mussel-class Intersection over Union [IoU] > 0.76) and density prediction (log-density R 2 = 0.79–0.95) over a variety of bottom types. AUV-based image acquisition is more than three orders of magnitude faster than physical sampling by divers or ponar grabs, and DNN-based analysis can proceed at rates comparable to image acquisition. We used MusselFinder to analyze over 50,000 spatially referenced images at a spawning reef in Lake Michigan, representing a shift from small-scale, diver-collected datasets to large-scale monitoring in unconstrained environments. The method can be adapted to new imaging conditions using a modest training set and a user-friendly point-labeling technique, supporting broader-scale monitoring of one of the world's most invasive invertebrates.

Illinois, Michigan↗

USGS2026

A spatial analysis of the groundwater emergence flood hazard in Long Island, New York, and coastal areas surrounding Long Island Sound in New York, Connecticut, and Rhode Island

Long Island, New York, and nearby coastal areas surrounding Long Island Sound are densely populated and, like other coastal areas, are susceptible to flooding from several potential sources, including stormwater from precipitation events, tidal flooding and storm surge, and groundwater emergence flooding. Groundwater emergence fooding refers to the intersection of a rising water table with land surface or critical infrastructure. Many studies of flood drivers either neglect or only briefly discuss how shallow groundwater conditions may contribute to or exacerbate flood conditions. As a part of a comprehensive study of compound flood hazards in the coastal areas of Long Island and Long Island Sound, a spatial analysis was completed by the U.S. Geological Survey, in cooperation with the Environmental Protection Agency’s Long Island Sound Partnership, formerly called the Long Island Sound Study, using available regional datasets to characterize the potential hazard for groundwater emergence flooding. The approximately 3,100 square mile study area was subdivided into 11,407 grid cells that were 900 meters by 900 meters (approximately 3,000 feet by 3,000 feet), for the purpose of integrating the spatial datasets to calculate and map the groundwater emergence flood hazard. The depth to the water table, hydrologic soil groups, and National Land Cover Database were harmonized to the common grid. A groundwater emergence flood hazard score was calculated for each grid cell for current average conditions following a set of rules accounting for the depth to the water table and the percentage of area within each cell with slow infiltrating soils. A scenario with a higher sea-level position was also calculated for the Long Island part of the study area. The calculated groundwater emergence flood hazard score was reviewed in conjunction with the National Land Cover Database to identify developed areas and associated infrastructure that may be at risk of potential groundwater emergence flooding. Study results indicate that the groundwater emergence flood hazard is highest in coastal areas and near surface water where the water table is close to ground surface. Inland areas away from surface waterbodies are not likely to be exposed to groundwater emergence flooding. For Long Island, in the scenario with higher sea-level position, a greater groundwater emergence flood hazard is calculated for some locations closer to the coast and where land is submerged. Away from the coast and surface-water drainage, the groundwater emergence flood hazard is similar between the current average sea-level condition and the higher sea-level position scenario.

Connecticut, New York, Rhode Island↗

USGS2026

Streamflow assessment of Birch Creek, southern boundary of the Blackfeet Indian Reservation, Pondera County, northwestern Montana—Synoptic and continuous streamflow measurements through 2022

The U.S. Geological Survey, in cooperation with the Blackfeet Water Department, performed this study to assist water-resource managers in understanding and quantifying irrigation diversions, instream flows, and the spatial and temporal streamflow dynamics of Birch Creek in northwestern Montana. Birch Creek forms the southernmost boundary of the Blackfeet Indian Reservation and is highly valued culturally as an aquatic life and wildlife resource and as a principal source of water for irrigation. The study area included Birch Creek from Swift Dam to 53.3 miles downstream just above its confluence with the Two Medicine River. The study period was calendar year 2022, but selected historical information was also included in the study. Birch Creek streamflow originates through releases from Swift Reservoir, with the largest releases typically occurring during the irrigation season (May–October) to primarily meet the needs of downstream irrigators. This study included the compilation and collection of (1) continuous streamflow measured at streamgages installed for this study, (2) instantaneous streamflow measurements made during four synoptic events, and (3) reported daily values of Swift Reservoir outflow and irrigation diversions. Continuous streamflow data were available from two U.S. Geological Survey streamgages: Birch Creek below Heart Butte Road, near Heart Butte, Montana (upper streamgage; station 06094900), at river mile 12.9 and Birch Creek at Bullhead Bridge near Valier, Mont. (lower streamgage; station 06098120), at river mile 53.3. The upper streamgage (station 06094900) was primarily affected by the regulated releases from Swift Dam with daily mean streamflow typically slightly higher than the reported Swift Reservoir outflows. Daily mean streamflow ranged from 9.87 cubic feet per second (ft 3 /s) (November 18, 2022) to 640 ft 3 /s (June 22, 2022) during September 16, 2021–December 31, 2022. The mean annual streamflow was 122 ft 3 /s in water year 2022 (a water year is the 12-month period from October 1 to September 30 and is designated by the year in which it ends), about 13 percent greater than the mean annual reported Swift Reservoir outflows. The lower streamgage (station 06098120) was downstream from all major tributaries and diversions within the Birch Creek drainage basin. Daily mean streamflow ranged from 6.02 ft 3 /s (September 8, 2022) to 95.0 ft 3 /s (June 5, 2021) during August 26, 2020–December 31, 2022. Mean annual streamflow was 27.8 ft 3 /s for water year 2022. Flows at the lower streamgage (station 06098120) were typically lower than at the upper streamgage (station 06094900) from late April to early October, whereas flows from early October to late spring were similar to or greater than those at the upper streamgage. The upper streamgage had a total streamflow volume of 87,960 acre-feet (acre-ft) for water year 2022, whereas the lower streamgage had a total streamflow of 20,357 acre-ft. A net volume of about 67,603 acre-ft was removed from Birch Creek through diversions, losses to groundwater, and evapotranspiration along that reach during water year 2022. Most of the changes in main-stem streamflow could be accounted for by the tributary inflows or diversion outflows. The most dynamic streamflow gains and losses occurred along the upper few miles of Birch Creek. Streamflow was consistently lost to the groundwater system immediately below Swift Dam and then returned to levels that slightly exceeded the outflow at the dam near river mile 11.0. The overall net gains for the entire 53.3-mile study reach ranged from 15.5 to 42.6 ft 3 /s among the synoptic events. On several occasions, streamflow fell below minimum instream flow conditions specified in the Blackfeet Compact (water rights compact among the Blackfeet Tribe, State of Montana, and United States), which are subject to a 15-year deferral period (until June 12, 2033). Notably, a section of Birch Creek immediately downstream from Swift Dam was completely dry during the October 18, 2022, synoptic event.

Montana↗

USGS2026

Humans experienced abrupt environmental changes at White Sands during the Last Glacial Maximum

Expanded excavations at White Sands National Park have unearthed 20 stratigraphic horizons containing in situ human footprints, megafaunal trackways, and linear features created by travois. Advances in radiocarbon dating of conifer pollen, combined with ages of aquatic seeds, refines the chronology of the footprint-bearing sequence to between 23.5 and 21.7 thousand years ago (ka). Biomarker, pollen, and stratigraphic evidence indicate a complete overturning of the environment from a perennial lake to a playa and capture a large aridification episode coincident with Dansgaard-Oeschger event 2 at 23.2 ka, which shrank pluvial Lake Otero and allowed people to traverse the former shoreline area for nearly two millennia. This well-dated and highly resolved paleoclimate record provides compelling evidence that humans in North America experienced marked environmental changes during the Last Glacial Maximum.

New Mexico↗

USGS2026

Terrain-based map of mélange and intact rock at the junction of Coastal and Central Belt rocks of the Franciscan Complex between Gualala and Ukiah, northern California Coast Ranges

A terrain-based map of a large area of Franciscan Complex between the San Andreas and Maacama faults east of Point Arena, California, provides much new detail compared to prior mapping. The new map reveals an unusual, structurally disrupted area that is defined by northwest-trending patches of erosionally resistant topography interspersed in subdued topography. These two terrain types, here termed Hard and Soft, are distinguished using differences in the detailed shapes of individual topographic elements that in these rocks are indicative of relatively intact rock and severely sheared mélange. The disrupted area lies at the junction between rocks of two different parts of the Franciscan Complex: sandstone and argillite of the Coastal belt to the northwest and mélange and variously metamorphosed sandstone and other rocks of the Central belt to the southeast. The rocks in the disrupted area seem to consist largely of Coastal belt sandstone interspersed in Central belt mélange. They are separated from areally continuous Coastal belt to the west by the newly defined Cedars fault and from continuous mélange of the Central belt to the east by the newly defined Boonville fault. A plausible history to account for Coastal belt rocks and Central belt mélange now interspersed at the same structural level in the disrupted area is westward thrusting of Central belt over Coastal belt on the Coastal belt thrust, located mostly above the present level of exposure, followed by extensional dip-slip faulting involving both the disrupted area and its bounding faults. Most of the study area has been mapped on the ground only in reconnaissance. The terrain map was prepared largely by interpretation of small-scale aerial photographs, with distinctions in the steepness of slopes and curvature of ridge and side-hill crests made from the photographs. These distinctions were then confirmed by differences in their areal abundance determined through quantitative mapping of slope and curvature. Most of the remainder of the map was prepared in the same fashion directly from the slope and curvature maps. Geologic identities are assigned to as much of the area as possible, but some resistant parts, mostly in the disturbed area, remain identified solely as Hard terrain. Some units, mostly along the southern edge of the map, are compiled from published sources. This report serves as a description and explanation of the associated spatial database (Wentworth, 2025), which consists of attributed line and polygon shape files and metadata describing them.

California↗