Coast Range Research Articles

Reflection seismic profiling along the Longitudinal Valley Basin, Eastern Taiwan: In search of the Central Range fault

A thorough understanding of the internal structures of the Longitudinal Valley is crucial for comprehending the architecture of the suture zone between the Eurasian and Philippine Sea plates. Here, we present the findings of eight new reflection seismic profiles spanning north to south of the Longitudinal Valley. Our primary objective is to investigate the internal sedimentary and tectonic features of the Longitudinal Valley Basin, the nature of the contact between it and the metamorphic basement rocks to the west, and the geometry of the Longitudinal Valley fault system along its eastern flank. A significant outcome of our research is that there is minimal internal deformation within the Longitudinal Valley Basin, with sedimentary features prevailing. The presence of inclined reflections suggests the presence of fan deltas and therefore a marine or lacustrine environment in the Longitudinal Valley. The sedimentary characteristics indicate that the source region for the sediment was predominately the Central Range, but that locally the Coastal Range also supplied sediment. Furthermore, at least in the shallow subsurface (1 to 2 km), a west-dipping Central Range fault does not exist along the western side of the Longitudinal Valley. The Longitudinal Valley fault system does not affect the middle of the basin, instead it is located along the eastern flank, adjoining the topography of the Coastal Range.

Subseasonal Clustering of Atmospheric Rivers Over the Western United States

AbstractThe serial occurrence of atmospheric rivers (ARs) along the US West Coast can lead to prolonged and exacerbated hydrologic impacts, threatening flood‐control and water‐supply infrastructure due to soil saturation and diminished recovery time between storms. Here a statistical approach for quantifying subseasonal temporal clustering among extreme events is applied to a 41‐year (1979–2019) wintertime AR catalog across the western United States (US). Observed AR occurrence, compared against a randomly distributed AR timeseries with the same average event density, reveals temporal clustering at a greater‐than‐random rate across the western US with a distinct geographical pattern. Compared to the Pacific Northwest, significant AR clusters over the northern Coastal Range of California and Sierra Nevada are more frequent and occur over longer time periods. Clusters along the California Coastal Range typically persist for 2 weeks, are composed of 4–5 ARs per cluster, and account for over 85% of total AR occurrence. Across the northwest Coast‐Cascade Ranges, clusters account for ∼50% of total AR occurrence, typically last 8–10 days, and contain 3–4 individual AR events. Based on precipitation data from a high‐resolution dynamical downscaling of reanalysis, the fractions of total and extreme hourly precipitation attributable to AR clusters are largest along the northern California coast and in the Sierra Nevada. Interannual variability among clusters highlights their importance for determining whether a particular water year is anomalously wet or dry. The mechanisms behind this unusual clustering are unclear and require further research.

Comparing diversity of the terrestrial mammal communities inhabiting native forests and exotic plantations in southern Chile

The mammal community of the Coastal Range of southern Chile has been little studied even though they inhabit an environment under severe threats due to anthropic disturbance. During the spring-summer seasons of 2020–2021 and 2021–2022, we characterized the communities of wild terrestrial mammals in a native forest (NF) and an exotic plantation of Eucalyptus (PL) of the Coastal Range of Osorno province by phototrapping. We used 1,060 camera-trap days in the NF and 960 camera-trap days in the PL to explore the effect of habitat type on wild mammal diversity in two localities (L-1 and L-2). We quantified the species richness, abundance, community similarity and daily distribution of mammal communities. Species richness was higher in the NF (7–8 spp) than in the PL (3–4 spp). Two community similarity index (CSI) was significantly higher between native forests (CSI = 0.728 ± 0.088) than between Eucalyptus plantations (CSI = 0.211 ± 0.097) (95% CI). Mean abundance was also higher in the NF than in the PL (L-1: 0.011 vs. 0.004 occurrence/camera-trap day (OCT); L-2: 0.008 vs. 0.004 OCT). In L-1, the most abundant mammals in the NF were Leopardus guigna (45.3% of relative occurrence (RO)) and Pudu puda (18.9% RO), and in the PL, they were Lycalopex culpaeus (50% RO) and L. guigna (37.5% RO). In L-2, the highest abundances in the NF were for P. puda (34.5% RO) and Puma concolor (27.6% RO), while in the PL, P. puda was predominant (66.7% RO). In NF of both localities, 22.2% of melanic L. guigna individuals were observed. The highest frequency of occurrences in both locations was between 12:00 and 23:59 hours, with 60% and 76.9% of detections, respectively. The species richness found in native forest is in accordance with studies carried out in other temperate rainforests of southern Chile. In addition, native forests support a richer and more similar community of terrestrial mammals than exotic forest plantations, which indicates that native forests are the main habitat for most mammals detected and that exotic plantations function as a complementary habitat for some species.

Deformation of the Juan de Fuca Plate Beneath the Central Cascadia Continental Margin (44°-45°N) in Response to an Upper Plate Load

A 3D crustal model for the central Cascadia continental shelf and Coast Range between 44°N and 45°N shows that the crystalline crust of the forearc wedge beneath the coastline is characterized by a NW-trending, vertical slab of high-velocity rock interpreted to represent the dike complex that fed the Yachats Basalt, which was intruded into the forearc approximately 37 million years ago. A spatial correlation is observed between downward deflection of the crust of the subducting Juan de Fuca plate, inferred from inversion of PmP arrivals to image the Moho surface, and the high velocity (and consequently high density) anomaly underlying the Yachats Basalt. Apparent subsequent rebound of the subducting plate at greater depth suggests a primarily elastic response of the subducting plate to this load. Calculations for a range of plausible values for the magnitude of the load and the width and depth of the depression indicate that the effective elastic thickness of the subducted Juan de Fuca plate is < 6 km. Although our simple analytical models do not include partial support of the load of the slab by the adjacent upper plate crust or time dependence to account for the motion of the slab beneath the load, incorporation of those effects should decrease rather than increase the apparent strength of the subducted plate. We conclude that the subducted Juan de Fuca plate beneath the central Oregon margin is elastically thin and has the potential to store elastic strain energy before rupturing. Our model of a well-defined, focused and static upper plate load that locally deforms the subducted plate within the nominally seismogenic or transitional part of the Cascadia plate boundary may be unique in providing a relatively straightforward scenario for estimating the mechanical properties of the subducted Juan de Fuca plate. We extrapolate from these results to speculate that elastic deformation of the subducting plate may contribute to the low level of seismicity throughout much of the Cascadia forearc in the inter-seismic period between great earthquakes but note that our local results do not preclude faulting or elasto-plastic deformation of a thin and weak plate as it subducts. These results also suggest that the subducting plate should deform in response to larger scale variations in upper plate thickness and density.

The importance of structural complexity in the localization of geothermal systems: A case study along the Vallès-Penedès Fault in the Catalan Coastal Ranges (NE Spain)

The Vallès-Penedès Fault is a Neogene normal fault marked by the presence of two established geothermal systems at La Garriga-Samalús and Caldes de Montbuí, within the Catalan Coastal Ranges (NE Spain). The analysis and collation of existing and new geological and geophysical datasets provide the basis for the development of an improved conceptual model that explains the presence and localization of hot geothermal fluid systems at relatively shallow depths (e.g., 60 °C at surface and 90 °C at 1 km). Geothermal flow is concentrated within Paleozoic granodiorites of the immediate footwall of the V-P fault, host rocks that are susceptible to fault-related fracturing, and the generation of both extension and hybrid fracture systems in association with active fault displacements. Flow localization is enhanced further by the presence of fault-related structural complexities, with both systems marked by 300 m wide steps in the main fault trace. These are attributed to relay development and breaching characterizing host rocks by high fracture intensities and fault rock development on a fault that locally has a vertical displacement of over 1.5 km. Accentuated fracturing and deformation are consistent with strain localization predicted by existing models for the development of fault zones along normal faults. The plumbing of the geothermal systems is attributed to up-fault flow in combination with lateral flow controlled by the intersection of the V-P fault with a low-angled Paleogene thrust defining the base of the host-rock granodiorites, with the geothermal systems localized at the distal end of the thrust. Sustained geothermal flow is attributed to groundwater flow circulation associated with seismic pumping and valving of warmer and deeper fluids, and the ingress of groundwater along faults and within fractured basement rocks.

Beetle evolution illuminates the geological history of the World's most diverse tropical archipelago

The geologically‐complex Indo–Australian–Melanesian archipelago (IAMA) hosts extraordinarily high levels of species richness and endemism and has long served as a natural laboratory for studying biogeography and evolution. Nonetheless, its geological history and the provenance and evolution of its biodiversity remain poorly understood. Here, we provide a geological scenario for the IAMA informed by a time‐calibrated molecular phylogeny of 1006 species of Trigonopterus weevils – an exceptionally diverse radiation of regionally‐endemic flightless beetles. Moreover, we performed a statistical biogeographic analysis and examined timing and patterns in the accumulation of lineages residing in a priori‐defined geographic units comprising the IAMA. We estimate that Trigonopterus originated in Australia during the early Paleogene. Subsequent rapid diversification in the area of the present‐day Papuan Peninsula suggests the presence of proto‐Papuan islands by the middle Eocene; the New Guinea North Coast Ranges were colonized in the late Eocene, followed by the New Guinea Highlands and the Bird's Head Peninsula. We inferred the presence of terrestrial habitat in the North Moluccas and Sulawesi in the late Oligocene and the subsequent rapid colonization of Sundaland and the Lesser Sunda Islands. New Caledonia and Samoa were colonized from the Papuan Peninsula, and their faunas also diverged in the late Oligocene. These biota‐informed time estimates are compatible with geological data from the region and shed new light on IAMA paleogeography, even where geological evidence has been lost to erosion. Beetle evolution thus appears to have closely tracked the geological evolution of the IAMA, revealing a uniquely well‐resolved view of regional biogeography.

PROBABILISTIC APPROACHES FOR ASSESSING EROSION HAZARD ALONG NEW SOUTH WALES MID NORTH COAST

A probabilistic shoreline hazard assessment has been undertaken for the Clarence Valley coastline on the Mid North Coast of New South Wales. The assessment was unique in its size and scope, implementing a detailed probabilistic methodology that spanned 70km of varying coastline, including a range of open coasts, embayed beaches, multiple headlands, river training walls, sand sources and sinks. It was designed to meet the requirements of the NSW Management Manual, for inclusion within an updated Coastal Management Program.

COMPARING RESPONSE-BASED AND EVENT-BASED OVERTOPPING DESIGN

Coastal structure crest elevations are routinely designed to a specific hazard level. In the U.S., for example, levee crest elevations often correspond to the 1 percent annual exceedance probability (AEP) overtopping rate at 90 percent confidence level (CL). Statistical methods to compute coastal structure response range from simply inputting wave and water level forcing conditions at a certain AEP into a response equation (i.e. event-based or frequency-based approach) to a fully stochastic Monte Carlo numerical simulation where thousands of storm responses are sampled and epistemic uncertainties incorporated (i.e. response-based approach). Event-based approaches oversimplify both statistics and physics; however, time, cost, and complexity can limit application of the response-based simulation. Response-based stochastic simulation approaches tend to more realistically characterize structure responses. Herein we compare common frequency-based and response-based stochastic approaches for levee and floodwall overtopping design. For frequency-based approaches, structure responses are computed using wave and water level forcings at a given AEP, and for response-based approaches, a large number of storms are sampled in a Monte Carlo simulation.

Records of the land planarian Polycladus gayi (Tricladida, Geoplanidae) preying on black snails Macrocyclis peruvianus (Gastropoda, Macrocyclidae)

AbstractPolycladus gayi is a colourful and easily recognizable land planarian native to the temperate to cold rainforests of the west coast of southern South America, in Chile and Argentina; however, its ecology is poorly understood. Here, we describe the first records of P. gayi preying on a black snail Macrocyclis peruvianus in the wild. Two events were recorded, the first in a healthy forest in Llancahue Alto, Panguipulli, Chile, during the austral summer of 2023, and the second in a mature evergreen forest in the coastal range of La Union, Chile. These records expand our knowledge of the feeding habits and behaviour of P. gayi and add M. peruvianus to its prey list.

Identification of non-conventional groundwater resources by means of machine learning in the Aconcagua basin, Chile

Study regionOur study region is the Aconcagua basin, central Chile. The catchment, home to over 500,000 people, currently experiences a multiyear drought that threatens water security. In this context, there is an impending need to explore unconventional groundwater resources, such as peripheral hard rock and deep aquifers. Study focusThe focus of this study is the application of machine learning techniques to identify areas of potentially untapped groundwater resources in the middle and upper reaches of the Aconcagua basin. New hydrological insights for the regionMachine learning classifiers accurately depict those areas known for their high groundwater potential, including the San Felipe, Putaendo, Panquehue, Catemu and Llay-Llay sectors. The Mesozoic sedimentary sequences and intrusive units of the coastal range, together with the Neogene units of the Andes range, are correctly identified as areas of very low hydrogeological interest. A major novelty of this study is the delineation of several new areas of potentially high groundwater prospect, namely, the geological domain associated with the Pocuro fault system, the Teatinos-Volcan-River fault system, and the Las Chilcas volcano-sedimentary sequence, in the Chacabuco Range. These findings are in line with the results of complementary studies, thus suggesting that machine learning applications may successfully underpin groundwater exploration across other groundwater basins in the coastal Andean region.

Subregional Anelastic Attenuation Model for California

ABSTRACT Ground-motion models (GMMs) typically include a source-to-site path model that describes the attenuation of ground motion with distance due to geometric spreading and anelastic attenuation. In contemporary GMMs, the anelastic component is typically derived for use in one or more broad geographical regions such as California or Japan, which necessarily averages spatially variable path effects within those regions. We extend that path modeling framework to account for systematic variations of anelastic attenuation for ten physiographic subregions in California that are defined in consideration of geological differences. Using a large database that is approximately doubled in size for California relative to Next Generation Attenuation (NGA)-West2, we find relatively high attenuation in Coast Range areas (North Coast, Bay area, and Central Coast), relatively low attenuation in eastern California (Sierra Nevada, eastern California shear zone), and state-average attenuation elsewhere, including southern California. As part of these analyses, we find for the North Coast region relatively weak ground motions on average from induced events (from the Geysers), similar attenuation rates for induced and tectonic events, and higher levels of ground-motion dispersion than other portions of the state. The proposed subregional path model appreciably reduces within-event and single-station variability relative to an NGA-West2 GMM for ground motions at large distance (RJB>100 km). The approach presented here can readily be adapted for other GMMs and regions.

Resilience of riparian vegetation productivity to early 21st century drought in northern California, USA

AbstractDrought and intensive land use can interact as stressors on riparian vegetation, especially along rivers flowing through seasonally dry landscapes. Knowledge of past riparian vegetation response to drought and land use change can provide land managers with a better understanding of changes induced by upstream management actions, climate change, and chronic stressors. To investigate the response of riparian vegetation productivity to drought and land use, we developed a 21‐year time series (2000–2020) of growing season vegetation dynamics using near‐infrared reflectance of vegetation (NIRV) derived from satellite data across 30 watershed subbasins that drain into the San Francisco Bay Delta in central California, USA. We observed a strong response of riparian vegetation to drought, but rapid recovery and very few long‐term declines in productivity. At a local level, vegetation communities' response to drought and post‐drought productivity dynamics were highly variable across biophysical settings and land use gradients. Most of the riparian areas with long‐term declines in NIRV were located in the lower elevation Coast Range on the western side of the study area where there is little to no water engineering or agricultural irrigation runoff to subsidize riparian vegetation. Riparian areas with the greatest long‐term increase were along rivers draining the higher elevation Sierra Nevada range to the east. Our results suggest that river systems with a high proportion of water originating as snowmelt may be more buffered against long‐term drought‐driven declines in productivity than those dependent exclusively on winter rainfall. The long‐term increase in NIRV in the vast majority of riparian areas within our study area may also have been driven in part by increasing atmospheric CO2 concentrations, which have been shown to increase plant water use efficiency.

Roccellinastrum, Cenozosia and Heterodermia: Ecology and phylogeny of fog lichens and their photobionts from the coastal Atacama Desert.

Some deserts on Earth such as the Namib or the Atacama are influenced by fog which can lead to the formation of local fog oases - unique environments hosting a great diversity of specialized plants and lichens. Lichens of the genera Ramalina, Niebla or Heterodermia have taxonomically been investigated from fog oases around the globe but not from the Atacama Desert, one of the oldest and driest deserts. Conditioned by its topography and the presence of orographic fog, the National Park Pan de Azúcar in the Atacama Desert is considered to be such a lichen hotspot. Applying multi-gen loci involving phylogenetic analyses combined with intense morphological and chemical characterization, we determined the taxonomic position of five of the most abundant epiphytic lichens of this area. We evaluated Roccellinastrumspongoideum and Heterodermiafollmannii which were both described from the area but also finally showed that the genus Cenozosia is the endemic sister genus to Ramalina, Vermilacinia, Namibialina and Niebla. As a result, we have described the species Heterodermiaadunca, C.cava and C.excorticata as new lichen species. This work provides a comprehensive dataset for common fog lichen genera of the Coastal Range of the Atacama Desert that can be used as a baseline for monitoring programs and environmental health assessments.

Agrostis swalalahos (Poaceae), a grass endemic to the mountains of northwest Oregon, U.S.A.

We describe a new grass species, Agrostis swalalahos, endemic to several peaks in the northwestern Coast Range of Clatsop County, Oregon, U.S.A.

Native Carnivore Diversity and Relative Abundance in Landscapes of the Coast Range in Central Chile: Insights for Conservation Decision-Making

Natural habitats in South America have been intensively used and modified, including their conversion to exotic tree plantations, impacting the terrestrial fauna communities. Carnivores play an important role in the functioning of ecosystems as apex predators. Landscape characteristics and resource availability determine the composition and abundance of co-occurring carnivores. We hypothesized that the diversity and relative abundance of native carnivores varied in relation to the different vegetation macrohabitats. We predicted that native forests support a higher diversity and abundance of native carnivores compared to exotic plantations. Between 1 March 2021 and 31 March 2022, we estimated the species’ richness, composition, and relative abundance of terrestrial native carnivores in three different landscapes of the Coast Range in central Chile: (a) monoculture plantation of the exotic Pinus radiata (MP); (b) Mediterranean coastal thorn forest (TF); and (c) Mediterranean coastal sclerophyllous forest (SF). We monitored an area of 1000 ha in each landscape, installing 10 camera traps (total of 30 camera traps). We used a monitoring transect with unbaited camera traps separated by 1 km, with a total photo-trapping effort of 10,046 camera days. The classification, organization, and analysis of camera trap data were conducted using CameraSweet software. The total number of independent native carnivore species events (photos separated > 60 min) recorded in each landscape were 1564 in SF, 1412 in TF, and 775 in MP. Carnivore richness and composition were not significantly different in all three landscapes. We detected five native carnivore species. Relative abundance by species was significantly higher in SF compared to MP for Leopardus guigna, Conepatus chinga, and Galictis cuja and also significantly higher in TF compared to MP for L. guigna. Our results suggest that the native vegetation cover must be preserved to maintain viable and abundant native carnivore populations, crucially relevant in the highly impacted and human-dominated global biodiversity hotspot of Central Chile. This study contributes to informing evidence-based decision-making and conservation strategies at the landscape level to mitigate biodiversity loss.

Adjacent and downstream effects of forest harvest on the distribution and abundance of larval headwater stream amphibians in the Oregon Coast Range

Forest harvest is a primary landscape-scale management action affecting riparian forests. Although concerns about impacts of forest harvest on stream amphibians is generally limited to areas adjacent to harvest, there is a paucity of information regarding potential downstream effects of forest harvest on these species. We designed a before-after, control-impact (BACI) experiment to quantify potential impacts of clearcut logging that included 12-m buffers or smaller variable-width buffers on the distribution and abundance of headwater stream amphibians in adjacent and downstream areas. We sampled larval coastal tailed frogs (Ascaphus truei), coastal giant salamanders (Dicamptodon tenebrosus), and Columbia torrent salamanders (Rhyacotriton kezeri) across 3,915 sampling occasions that spanned 13 study reaches in 2008–2011 (pre-harvest) and 2013–2016 (post-harvest) as part of the Trask River Watershed Study in the Oregon Coast Range, U.S.A. We analyzed these data using occupancy models to estimate occupancy and (when possible) relative abundance, while accounting for various sources of imperfect detection. All species exhibited reduced occupancy adjacent to clearcuts with variable-width buffers (odds ratios [ORs] ranged = 0.24–0.48), and these negative impacts were not always diminished when increasing the buffer size to 12 m (ORs ranged = 0.20–3.56). Dicamptodon tenebrosus was the only species to have occupancy impacted in downstream areas, and this negative impact was related to clearcut logging with uniform 12-m buffers (OR = 0.60). This species was also the only species to have abundance negatively impacted by forest harvest in downstream areas (OR = 0.41 with uniform 12-m buffers, OR = 0.38 with variable-width buffers), albeit impacts to abundance were not evaluated for R. kezeri. Ascaphus truei abundance increased in areas downstream of clearcut logging with uniform 12-m buffers (OR = 2.92). Although we found the direction and magnitude of responses varied by species, our study confirms that clearcut logging can have negative impacts on amphibians that inhabit the adjacent stream areas. Perhaps more importantly, we also found that forest harvest can have negative effects on stream amphibians downstream of the harvested area and that increasing the buffer size to 12 m did not necessarily diminish these impacts in adjacent and downstream areas. Altogether, our study provides a nuanced picture of adjacent and downstream effects of forest harvest on three endemic headwater stream amphibians, and our findings demonstrate that forest management practices should consider downstream effects on aquatic taxa when assessing the impact of harvesting trees near headwater streams.

Integrated Zoning and Spatial Heterogeneity of Coastal Watershed-Nearshore Waters

Integrated land-sea development and protection are important for the sustainable development of coastal areas. To promote the transition from separate land-sea management to integrated land-sea governance, the scientific delineation of the integrated spatial zoning units of coastal watershed-nearshore waters is an important tool for integrated land-sea management. From the perspective of physical geography, this study uses digital hydrological analysis based on DEM data to determine the coastal basin range and generate multilevel watersheds and river networks using different thresholds, and establishes spatial correspondence among physical geospatial spaces, such as watershed zones, coastlines, and nearshore waters, after considering the boundaries of major estuaries and bays. On this basis, the coastal zone is divided into several integrated spatial zoning units of coastal watershed-nearshore waters, and a physical geography-based integrated spatial zoning method is developed to form a physical geography-based land-sea integrated spatial zoning scheme. This study conducted spatial heterogeneity research of the integrated spatial zoning units, from the perspectives of topography analysis, land use analysis, socioeconomic analysis of the watershed, sea use analysis, seawater quality analysis of the nearshore waters, and load pressure analysis of the watershed-nearshore waters. The elemental differences of zoning units are studied in detail, which can provide a data reference for establishing the relationship between watersheds and nearshore waters. Applying this research method to the Guangxi Zhuang Autonomous Region in China, where the land-sea linkage pattern is forming, can provide a spatial reference and scientific basis for land-sea integrated management for ecological protection and sustainable resource utilization in the coastal zone.

The geoelectric field coast effect: Results from two dimensional finite element method and analytic solutions

The geoelectric fields induced during geomagnetic disturbances (GMD) may affect the normal operation of technological systems at the Earth’s surface. The non-uniform Earth conductivity structure, especially large lateral conductivity contrasts, can lead to the enhancement of geoelectric fields near boundaries such as a coastline. In this paper, we give an overview of the applicability of a two-dimensional finite element method (2D-FEM) for studying lateral variations of the Earth’s conductivity, which can be considered as one of magnetotelluric sounding forward modelling methods, including both the E and the H polarization cases. Then the spatial distribution of the geoelectric field near a continent-ocean boundary is calculated with different models. This is compared with analytic solutions for simple models to verify the accuracy of the FEM modelling, which is calculated by using the ANSOFT software. More realistic scenarios are then developed to emphasize the advantages of FEM. The factors influencing the coast effect are discussed. Results show that frequency, the shape of seafloor boundaries, and the depth of ocean have a significant impact on the geoelectric fields. Therefore, these factors should attract more attention when assessing risk for man-made conducting systems located within the coastal influence range.

Mapping Variations in Bedrock Weathering With Slope Aspect Under a Sedimentary Ridge‐Valley System Using Near‐Surface Geophysics and Drilling

AbstractUnderstanding how soil thickness and bedrock weathering vary across ridge and valley topography is needed to constrain the flowpaths of water and sediment production within a landscape. Here, we investigate saprolite and weathered bedrock properties across a ridge‐valley system in the Northern California Coast Ranges, USA, where topography varies with slope aspect such that north‐facing slopes have thicker soils and are more densely vegetated than south‐facing slopes. We use active source seismic refraction surveys to extend observations made in boreholes to the hillslope scale. Seismic velocity models across several ridges capture a high velocity gradient zone (from 1,000 to 2,500 m/s) located ∼4–13 m below ridgetops that coincides with transitions in material strength and chemical depletion observed in boreholes. Comparing this transition depth across multiple north‐ and south‐facing slopes, we find that the thickness of saprolite does not vary with slope aspects. Additionally, seismic survey lines perpendicular and parallel to bedding planes reveal weathering profiles that thicken upslope and taper downslope to channels. Using a rock physics model incorporating seismic velocity, we estimate the total porosity of the saprolite and find that inherited fractures contribute a substantial amount of pore space in the upper 6 m, and the lateral porosity structure varies strongly with hillslope position. The aspect‐independent weathering structure suggests that the contemporary critical zone structure at Rancho Venada is a legacy of past climate and vegetation conditions.

DR. THOMAS ANTISELL (1817–1893): 19th CENTURY MEDICAL GEOLOGIST

ABSTRACT In America, Dr. Thomas Antisell (1817–1893) is best known for his work as a geologist with the Pacific Railroad Survey under Lt. Parke. Prior to his participation with the survey, his background was in medicine, chemistry and geology, with accomplishments in all three areas, notably writing on the geology and soils of his native Ireland. As a political outcast, his arrival in America in 1854 found him teaching chemistry and practicing medicine, until his relationship with fellow Irish botanist and physician John Torrey landed him a position as geologist with that part of the survey exploring portions of southern California, notably the Coastal Range, and southern portions of Arizona and New Mexico. Although his involvement with the survey would be his last large-scale federally-sponsored geological endeavor, he would continue to pursue interests in applied geology, among his other varied interests in medicine and chemistry. These interests would include federal positions as Chemical Examiner with the United States Patent Office, Capital Chemist with the United States Department of Agriculture, surgeon during the Civil War, consultant as a Foreign Advisor in Japan, and Professor at Georgetown University, among other schools of medicine. Although many early American geologists received their academic education at medical schools, and were physicians that made career moves to geology and remained professional geologists throughout their career, Antisell was primarily a physician, with varied interests in applied chemistry and applied geology as evident from his writings. Thus, Antisell is one of America’s early Medical Geologists; a term that would not become familiar and commonplace to the geological community until the 1990s. Moreover, as with other geologists of his time, he got some things right, and others not so, but his work set a geological foundation in new regions of the country, and raised questions that would eventually be addressed more fully by later investigators.