Harrison Gray, Ph.D
Earth's surface is shaped by the transfer of sediment across time and space. As we live on the Earth's surface, understanding this transport of sediment is key to the well-being of our species. I work on solving problems asscociated with landscapes and sediment transport using the tools of computer landscape evolution modeling and the trapped-charge phenomena known as luminescence.
Education and Certifications
Ph.D Geomorphology, University of Colorado - Boulder, 2018
M.S. Geology, Univeristy of Cincinnati, 2013
B.S. Earth Sciences, University of California - Santa Cruz, 2010
Honors and Awards
Presidential Early Career Award for Scientists and Engineers (PECASE), 2025
Science and Products
Earthquake Geology and Paleoseismology Overview
The goals of USGS earthquake geology and paleoseismology research are 1) to make primary observations and develop ideas to improve our understanding of the geologic expression of active faulting, and 2) to acquire data that will improve the National Seismic Hazard Model. Geological research allows us to characterize faults, including the identification of secondary seismogenic structures, to study...
Quaternary Hydroclimate Records of Spring Ecosystems
Desert springs and wetlands are among the most biologically productive, diverse, and fragile ecosystems on Earth. They are home to thousands of rare, endemic, and endangered plants and animals and reflect the availability and health of emergent groundwater. Despite the ecological importance of these wetlands, our knowledge of how they might respond to future environmental conditions is limited...
Western Basin & Range - Eastern California Shear Zone
The Eastern California Shear Zone (ECSZ) Mapping project, funded by the National Cooperative Geologic Mapping Program, combines surficial and bedrock geologic mapping, geophysical surveys, and high-resolution topographic data analysis with neotectonic, geomorphic, structural, volcanic, and geochronologic studies to better understand the tectonic framework and landscape evolution of the ECSZ in the...
Filter Total Items: 13
Data Release for Timing and Abandonment of the Chemehuevi Formation: a Conspicuous Pleistocene Sedimentary Deposit of the Lower Colorado River Data Release for Timing and Abandonment of the Chemehuevi Formation: a Conspicuous Pleistocene Sedimentary Deposit of the Lower Colorado River
This data release contains data for the associated publication: Timing and Abandonment of the Chemehuevi Formation: a Conspicuous Pleistocene Sedimentary Deposit of the Lower Colorado River
Data Release for Luminescence: Neotectonic Mapping of Puerto Rico Data Release for Luminescence: Neotectonic Mapping of Puerto Rico
This report details the luminescence ages and characteristics of four (4) samples that were collected by Jessica Jobe and Rich Briggs of the USGS. These samples are from Holocene and Pleistocene sediments offset by a fault that is exposed in a road cut. The roadcut is in Puerto Rico at 18.003828 and -67.140249 with an elevation of 13.5 m. The sample depths from the modern surface varied...
Datasets documenting neotectonic mapping of Puerto Rico Datasets documenting neotectonic mapping of Puerto Rico
This data release documents neotectonic mapping of fault-related features on high-resolution lidar-derived topography, data documenting an exposure of the South Lajas fault, and summary information for active and potentially active Quaternary faults on the island of Puerto Rico. The data documenting the exposure of the South Lajas fault include detailed unit descriptions, radiocarbon...
Data release for Independent age estimates resolve the controversy of ancient human footprints at White Sands Data release for Independent age estimates resolve the controversy of ancient human footprints at White Sands
Human footprints at White Sands National Park, New Mexico, USA, reportedly date to between ~23,000 and 21,000 years ago according to radiocarbon dating of seeds from the aquatic plant Ruppia cirrhosa. These ages remain controversial because of potential old carbon reservoir effects that could compromise their accuracy. We present new calibrated 14C ages of terrestrial pollen collected...
Geochronologic and isotopic data for Paleohydrologic history of Pluvial Lake San Agustin, New Mexico Geochronologic and isotopic data for Paleohydrologic history of Pluvial Lake San Agustin, New Mexico
This dataset includes tables of radiocarbon, uranium thorium series, and luminescence geochronologic ages and stable carbon and oxygen isotope compositions for sedimentary and organic samples.
Geochronological Data for the Deep Creek paleoseismic site, Wasatch fault zone, Utah Geochronological Data for the Deep Creek paleoseismic site, Wasatch fault zone, Utah
This data release includes geochronological data for a natural exposure of the Wasatch fault, Utah at the Deep Creek site (39.507462?, -111.861790?). Laboratory data include 11 optically stimulated luminescence (OSL) ages for quartz, 23 charcoal radiocarbon ages, and 342 portable OSL (bulk luminescence) measurements. The radiocarbon and luminescence samples were collected November 2019...
Data Release for Luminescence: Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: examples from the western Sangre de Cristo Mountains, south-central Colorado Data Release for Luminescence: Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: examples from the western Sangre de Cristo Mountains, south-central Colorado
The following report summarizes the dating results from the San Luis Valley-Pioneer Fan 2017-2019 dating project. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and dating-related calculations. We recommend that this report be...
Data Release for Luminescence: Mid to Late Quaternary Geomorphic and Paleoseismic Event History, Cheraw Fault, Colorado Data Release for Luminescence: Mid to Late Quaternary Geomorphic and Paleoseismic Event History, Cheraw Fault, Colorado
Despite its subdued expression and isolated location within the Great Plains of southeastern Colorado, the 80-km-long Cheraw fault may be one of the most active faults in North America east of the Southern Rocky Mountains. We present geomorphic analyses, geochronology, and paleoseismic trenching data to 1) document the rupture history of the ~45-km-long southwestern section of the Cheraw...
Data Release for Luminescence: Floodplain Sediment Storage Timescales of the Laterally Confined Meandering Powder River, U.S.A Data Release for Luminescence: Floodplain Sediment Storage Timescales of the Laterally Confined Meandering Powder River, U.S.A
The following report summarizes the dating results from the. Within this report, we detail the methodology used to determine the storage time distribution for a 17 km length of Powder River in Montana, U.S.A. by the age distribution of eroded sediment. This data is used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence...
Data release for luminescence: Edwards Air Force Base (CA) and CA Water Science Center report including luminescence data and ages Data release for luminescence: Edwards Air Force Base (CA) and CA Water Science Center report including luminescence data and ages
The following report summarizes the dating results from Aeolian deposits within and around Edwards Air Force Base in California. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and dating related calculations. We recommend that...
DATA RELEASE Part 2: Optical luminescence dating of Bradley Lake, Oregon, tsunami deposits, analytical data for: A maximum rupture model for the central and southern Cascadia subduction zone-reassessing ages for coastal evidence of megathrust earthquakes DATA RELEASE Part 2: Optical luminescence dating of Bradley Lake, Oregon, tsunami deposits, analytical data for: A maximum rupture model for the central and southern Cascadia subduction zone-reassessing ages for coastal evidence of megathrust earthquakes
The following report summarizes the dating results from Bradley Lake, Oregon. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and datingrelated calculations. We recommend that this report be included as the supplementary...
Luminescence, weather, and grain-size data from eastern Chuckwalla Valley, Riverside County, California Luminescence, weather, and grain-size data from eastern Chuckwalla Valley, Riverside County, California
This data release contains luminescence, weather, and sediment grain-size data from eastern Chuckwalla Valley, Riverside County, California. This study investigates sedimentary and geomorphic processes in eastern Chuckwalla Valley, Riverside County, California, a region of arid, basin-and-range terrain where extensive solar-energy development is planned. The objectives were to (1)...
Filter Total Items: 28
Spatiotemporal variations in strain release and seismic rupture in multifault systems: An example from Panamint Valley, southeastern California Spatiotemporal variations in strain release and seismic rupture in multifault systems: An example from Panamint Valley, southeastern California
Geometrically complex, multifault ruptures have been observed in recent, damaging earthquakes in southeastern California, sparking renewed efforts to identify physical conditions that promote or inhibit fault discontinuity-spanning coseismic ruptures. The likelihood of ruptures propagating across fault discontinuities is thought to be partly controlled by fault geometries, rupture...
Authors
Aubrey LaPlante, Christine Regalla, Israporn Sethanant, Shannon Mahan, Harrison J. Gray
Evidence for nonlocal sediment transport on hillslopes from fault scarp morphology Evidence for nonlocal sediment transport on hillslopes from fault scarp morphology
Hillslope sediment transport processes such as bioturbation, rainsplash, and granular mechanics occur across the entire planet. Yet, it remains uncertain how these small-scale processes act together to shape landscapes. Longstanding hillslope diffusion theory posits that hillslope processes are spatially limited, whereas new concepts of nonlocal sediment transport argue otherwise...
Authors
Harrison J. Gray, Tyler Doane, Sylvia Nicovich, Christopher DuRoss, Ryan Gold
Timing and geometry of the Chemehuevi Formation reveal a late Pleistocene sediment pulse into the Lower Colorado River Timing and geometry of the Chemehuevi Formation reveal a late Pleistocene sediment pulse into the Lower Colorado River
The Chemehuevi Formation is a distinctive 50−150-m-thick wedge-shaped Pleistocene sedimentary unit deposited by the Colorado River. It lines the perimeters of the river’s floodplains and bedrock canyons for more than 600 km between the mouth of the Grand Canyon and the delta region in the Gulf of California. The formation is composed of a basal tan to light-yellowish-brown and pale...
Authors
Harrison J. Gray, Kyle House, Adam Hudson, Jorge Vazquez, Ryan Crow, Miriam Primus, Shannon Mahan, Tammy Rittenour, Keith A. Howard
Neotectonic mapping of Puerto Rico Neotectonic mapping of Puerto Rico
Puerto Rico is part of the Puerto Rico-Virgin Islands microplate, along the Caribbean–North American plate boundary between the Puerto Rico trench subduction zone and the Muertos Trough incipient subduction zone. Despite recent seismicity and geodetically constrained deformation of ~3 mm/yr of left-lateral shear across the island, Quaternary fault locations remain largely uncertain...
Authors
Jessica Jobe, Richard Briggs, K. Hughes, J. Joyce, Ryan Gold, Shannon Mahan, Harrison J. Gray, Laura Strickland
The geochronology of White Sands Locality 2 is resolved The geochronology of White Sands Locality 2 is resolved
Rhode et al. (2024) allege that there are many “unresolved issues” with the geochronology of White Sands National Park (WHSA) Locality 2. They suggest there are substantial age offsets due to hard-water effects in the aquatic plants that were dated and that radiocarbon ages of pollen may be anomalously old due to reworking. In their view, the luminescence ages are likely to be maximum...
Authors
Jeffrey Pigati, Kathleen Springer, Harrison J. Gray, Matthew Bennett, David Bustos
High-resolution geophysical and geochronological analysis of a relict shoreface deposit offshore central California: Implications for slip rate along the Hosgri fault High-resolution geophysical and geochronological analysis of a relict shoreface deposit offshore central California: Implications for slip rate along the Hosgri fault
The Cross-Hosgri slope is a bathymetric lineament that crosses the main strand of the Hosgri fault offshore Point Estero, central California. Recently collected chirp seismic reflection profiles and sediment cores provide the basis for a reassessment of Cross-Hosgri slope origin and the lateral slip rate of the Hosgri fault based on offset of the lower slope break of the Cross-Hosgri...
Authors
Jared W. Kluesner, Samuel Y. Johnson, Stuart P. Nishenko, Elisa Medri, Alex Simms, Gary Greene, Harrison J. Gray, Shannon Mahan, Jason Padgett, Emma Krolczyk, Daniel S. Brothers, James Conrad
Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: Examples from the western Sangre de Cristo Mountains, south-central Colorado Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: Examples from the western Sangre de Cristo Mountains, south-central Colorado
Debris-flow alluvial fans are iconic features of dynamic landscapes and are hypothesized to record tectonic and climatic change. Here, we highlight their complex formation and evolution through an exemplary suite of Quaternary debris-flow alluvial fans emanating from the western range front of the Sangre de Cristo Mountains in south-central Colorado, USA. To evaluate the constructive and...
Authors
Sylvia Nicovich, James Schmitt, Harrison J. Gray, Ralph Klinger, Shannon Mahan
Independent age estimates resolve the controversy of ancient human footprints at White Sands Independent age estimates resolve the controversy of ancient human footprints at White Sands
Human footprints at White Sands National Park, New Mexico, USA, reportedly date to between ~23,000 and 21,000 years ago according to radiocarbon dating of seeds from the aquatic plant Ruppia cirrhosa. These ages remain controversial because of potential old carbon reservoir effects that could compromise their accuracy. We present new calibrated 14C ages of terrestrial pollen collected...
Authors
Jeffrey Pigati, Kathleen Springer, Jeffrey Honke, David Wahl, Marie Champagne, Susan Zimmerman, Harrison J. Gray, Vincent Santucci, Daniel Odess, David Bustos, Matthew Bennett
Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition
Paleoclimate records across the Intermountain West region of North America show significant regional variation in timing and magnitude of wet conditions that accompanied the last glacial-interglacial transition. To understand the climate controls on paleohydrologic change, well-dated records are needed across the region. The Plains of San Agustin (New Mexico, USA) is a closed-basin...
Authors
Adam Hudson, Jay Quade, Vance Holliday, Brendan Fenerty, Jordon Bright, Harrison Gray, Shannon Mahan
Luminescence sediment tracing reveals the complex dynamics of colluvial wedge formation Luminescence sediment tracing reveals the complex dynamics of colluvial wedge formation
Paleoearthquake studies that inform seismic hazard rely on assumptions of sediment transport that remain largely untested. Here, we test a widespread conceptual model and a new numerical model on the formation of colluvial wedges, a key deposit used to constrain the timing of paleoearthquakes. We perform this test by applying luminescence, a sunlight-sensitive sediment tracer, at a field...
Authors
Harrison J. Gray, Christopher DuRoss, Sylvia Nicovich, Ryan Gold
A geomorphic-process-based cellular automata model of colluvial wedge morphology and stratigraphy A geomorphic-process-based cellular automata model of colluvial wedge morphology and stratigraphy
The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding...
Authors
Harrison J. Gray, Christopher DuRoss, Sylvia Nicovich, Ryan Gold
How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)? How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)?
We excavated trenches at two paleoseismic sites bounding a trans-basin bedrock ridge (the Willow Creek Hills) along the northern Lost River fault zone to explore the uniqueness of the 1983 Mw 6.9 Borah Peak earthquake compared to its prehistoric predecessors. At the Sheep Creek site on the southernmost Warm Springs section, two earthquakes occurred at 9.8−14.0 ka (95% confidence) and 6.5...
Authors
Christopher DuRoss, Richard Briggs, Ryan Gold, Alexandra Hatem, Austin Elliott, Jaime Delano, Ivan Medina-Cascales, Harrison J. Gray, Shannon Mahan, Sylvia Nicovich, Zachery Lifton, Emily Kleber, Greg McDonald, Adam Hiscock, Mike Bunds, Nadine Reitman
Geologic Stories in Grand Canyon Geologic Stories in Grand Canyon
Take a trip through Grand Canyon with USGS geologists to learn about geologic mapping in this iconic landscape. On the trip, scientists from Arizona, New Mexico, California and Colorado also conducted a series of related research studies to inform the geologic maps and geologic history of Grand Canyon.
By
Core Science Systems Mission Area, Water Resources Mission Area, Environmental Health Program, National Cooperative Geologic Mapping Program, National Water Quality Program, Toxic Substances Hydrology, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center, New Mexico Water Science Center, Southwest Biological Science Center, Denver Radiogenic Isotope Lab, Mineralogy and Microscopy Laboratory, New Mexico Water Science Center Sediment Laboratory, Organic Geochemistry Laboratory, Geological Materials Repository, Geology and Ecology of National Parks, National Hydrography, Science Data Management, Colorado River Basin: Actionable and Strategic Integrated Science and Technology
Science and Products
Earthquake Geology and Paleoseismology Overview
The goals of USGS earthquake geology and paleoseismology research are 1) to make primary observations and develop ideas to improve our understanding of the geologic expression of active faulting, and 2) to acquire data that will improve the National Seismic Hazard Model. Geological research allows us to characterize faults, including the identification of secondary seismogenic structures, to study...
Quaternary Hydroclimate Records of Spring Ecosystems
Desert springs and wetlands are among the most biologically productive, diverse, and fragile ecosystems on Earth. They are home to thousands of rare, endemic, and endangered plants and animals and reflect the availability and health of emergent groundwater. Despite the ecological importance of these wetlands, our knowledge of how they might respond to future environmental conditions is limited...
Western Basin & Range - Eastern California Shear Zone
The Eastern California Shear Zone (ECSZ) Mapping project, funded by the National Cooperative Geologic Mapping Program, combines surficial and bedrock geologic mapping, geophysical surveys, and high-resolution topographic data analysis with neotectonic, geomorphic, structural, volcanic, and geochronologic studies to better understand the tectonic framework and landscape evolution of the ECSZ in the...
Filter Total Items: 13
Data Release for Timing and Abandonment of the Chemehuevi Formation: a Conspicuous Pleistocene Sedimentary Deposit of the Lower Colorado River Data Release for Timing and Abandonment of the Chemehuevi Formation: a Conspicuous Pleistocene Sedimentary Deposit of the Lower Colorado River
This data release contains data for the associated publication: Timing and Abandonment of the Chemehuevi Formation: a Conspicuous Pleistocene Sedimentary Deposit of the Lower Colorado River
Data Release for Luminescence: Neotectonic Mapping of Puerto Rico Data Release for Luminescence: Neotectonic Mapping of Puerto Rico
This report details the luminescence ages and characteristics of four (4) samples that were collected by Jessica Jobe and Rich Briggs of the USGS. These samples are from Holocene and Pleistocene sediments offset by a fault that is exposed in a road cut. The roadcut is in Puerto Rico at 18.003828 and -67.140249 with an elevation of 13.5 m. The sample depths from the modern surface varied...
Datasets documenting neotectonic mapping of Puerto Rico Datasets documenting neotectonic mapping of Puerto Rico
This data release documents neotectonic mapping of fault-related features on high-resolution lidar-derived topography, data documenting an exposure of the South Lajas fault, and summary information for active and potentially active Quaternary faults on the island of Puerto Rico. The data documenting the exposure of the South Lajas fault include detailed unit descriptions, radiocarbon...
Data release for Independent age estimates resolve the controversy of ancient human footprints at White Sands Data release for Independent age estimates resolve the controversy of ancient human footprints at White Sands
Human footprints at White Sands National Park, New Mexico, USA, reportedly date to between ~23,000 and 21,000 years ago according to radiocarbon dating of seeds from the aquatic plant Ruppia cirrhosa. These ages remain controversial because of potential old carbon reservoir effects that could compromise their accuracy. We present new calibrated 14C ages of terrestrial pollen collected...
Geochronologic and isotopic data for Paleohydrologic history of Pluvial Lake San Agustin, New Mexico Geochronologic and isotopic data for Paleohydrologic history of Pluvial Lake San Agustin, New Mexico
This dataset includes tables of radiocarbon, uranium thorium series, and luminescence geochronologic ages and stable carbon and oxygen isotope compositions for sedimentary and organic samples.
Geochronological Data for the Deep Creek paleoseismic site, Wasatch fault zone, Utah Geochronological Data for the Deep Creek paleoseismic site, Wasatch fault zone, Utah
This data release includes geochronological data for a natural exposure of the Wasatch fault, Utah at the Deep Creek site (39.507462?, -111.861790?). Laboratory data include 11 optically stimulated luminescence (OSL) ages for quartz, 23 charcoal radiocarbon ages, and 342 portable OSL (bulk luminescence) measurements. The radiocarbon and luminescence samples were collected November 2019...
Data Release for Luminescence: Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: examples from the western Sangre de Cristo Mountains, south-central Colorado Data Release for Luminescence: Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: examples from the western Sangre de Cristo Mountains, south-central Colorado
The following report summarizes the dating results from the San Luis Valley-Pioneer Fan 2017-2019 dating project. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and dating-related calculations. We recommend that this report be...
Data Release for Luminescence: Mid to Late Quaternary Geomorphic and Paleoseismic Event History, Cheraw Fault, Colorado Data Release for Luminescence: Mid to Late Quaternary Geomorphic and Paleoseismic Event History, Cheraw Fault, Colorado
Despite its subdued expression and isolated location within the Great Plains of southeastern Colorado, the 80-km-long Cheraw fault may be one of the most active faults in North America east of the Southern Rocky Mountains. We present geomorphic analyses, geochronology, and paleoseismic trenching data to 1) document the rupture history of the ~45-km-long southwestern section of the Cheraw...
Data Release for Luminescence: Floodplain Sediment Storage Timescales of the Laterally Confined Meandering Powder River, U.S.A Data Release for Luminescence: Floodplain Sediment Storage Timescales of the Laterally Confined Meandering Powder River, U.S.A
The following report summarizes the dating results from the. Within this report, we detail the methodology used to determine the storage time distribution for a 17 km length of Powder River in Montana, U.S.A. by the age distribution of eroded sediment. This data is used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence...
Data release for luminescence: Edwards Air Force Base (CA) and CA Water Science Center report including luminescence data and ages Data release for luminescence: Edwards Air Force Base (CA) and CA Water Science Center report including luminescence data and ages
The following report summarizes the dating results from Aeolian deposits within and around Edwards Air Force Base in California. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and dating related calculations. We recommend that...
DATA RELEASE Part 2: Optical luminescence dating of Bradley Lake, Oregon, tsunami deposits, analytical data for: A maximum rupture model for the central and southern Cascadia subduction zone-reassessing ages for coastal evidence of megathrust earthquakes DATA RELEASE Part 2: Optical luminescence dating of Bradley Lake, Oregon, tsunami deposits, analytical data for: A maximum rupture model for the central and southern Cascadia subduction zone-reassessing ages for coastal evidence of megathrust earthquakes
The following report summarizes the dating results from Bradley Lake, Oregon. Within this report, we detail the methodology used by the USGS Luminescence Geochronology Laboratory to obtain ages including sample preparation methods, luminescence measurement, equivalent dose determination, and datingrelated calculations. We recommend that this report be included as the supplementary...
Luminescence, weather, and grain-size data from eastern Chuckwalla Valley, Riverside County, California Luminescence, weather, and grain-size data from eastern Chuckwalla Valley, Riverside County, California
This data release contains luminescence, weather, and sediment grain-size data from eastern Chuckwalla Valley, Riverside County, California. This study investigates sedimentary and geomorphic processes in eastern Chuckwalla Valley, Riverside County, California, a region of arid, basin-and-range terrain where extensive solar-energy development is planned. The objectives were to (1)...
Filter Total Items: 28
Spatiotemporal variations in strain release and seismic rupture in multifault systems: An example from Panamint Valley, southeastern California Spatiotemporal variations in strain release and seismic rupture in multifault systems: An example from Panamint Valley, southeastern California
Geometrically complex, multifault ruptures have been observed in recent, damaging earthquakes in southeastern California, sparking renewed efforts to identify physical conditions that promote or inhibit fault discontinuity-spanning coseismic ruptures. The likelihood of ruptures propagating across fault discontinuities is thought to be partly controlled by fault geometries, rupture...
Authors
Aubrey LaPlante, Christine Regalla, Israporn Sethanant, Shannon Mahan, Harrison J. Gray
Evidence for nonlocal sediment transport on hillslopes from fault scarp morphology Evidence for nonlocal sediment transport on hillslopes from fault scarp morphology
Hillslope sediment transport processes such as bioturbation, rainsplash, and granular mechanics occur across the entire planet. Yet, it remains uncertain how these small-scale processes act together to shape landscapes. Longstanding hillslope diffusion theory posits that hillslope processes are spatially limited, whereas new concepts of nonlocal sediment transport argue otherwise...
Authors
Harrison J. Gray, Tyler Doane, Sylvia Nicovich, Christopher DuRoss, Ryan Gold
Timing and geometry of the Chemehuevi Formation reveal a late Pleistocene sediment pulse into the Lower Colorado River Timing and geometry of the Chemehuevi Formation reveal a late Pleistocene sediment pulse into the Lower Colorado River
The Chemehuevi Formation is a distinctive 50−150-m-thick wedge-shaped Pleistocene sedimentary unit deposited by the Colorado River. It lines the perimeters of the river’s floodplains and bedrock canyons for more than 600 km between the mouth of the Grand Canyon and the delta region in the Gulf of California. The formation is composed of a basal tan to light-yellowish-brown and pale...
Authors
Harrison J. Gray, Kyle House, Adam Hudson, Jorge Vazquez, Ryan Crow, Miriam Primus, Shannon Mahan, Tammy Rittenour, Keith A. Howard
Neotectonic mapping of Puerto Rico Neotectonic mapping of Puerto Rico
Puerto Rico is part of the Puerto Rico-Virgin Islands microplate, along the Caribbean–North American plate boundary between the Puerto Rico trench subduction zone and the Muertos Trough incipient subduction zone. Despite recent seismicity and geodetically constrained deformation of ~3 mm/yr of left-lateral shear across the island, Quaternary fault locations remain largely uncertain...
Authors
Jessica Jobe, Richard Briggs, K. Hughes, J. Joyce, Ryan Gold, Shannon Mahan, Harrison J. Gray, Laura Strickland
The geochronology of White Sands Locality 2 is resolved The geochronology of White Sands Locality 2 is resolved
Rhode et al. (2024) allege that there are many “unresolved issues” with the geochronology of White Sands National Park (WHSA) Locality 2. They suggest there are substantial age offsets due to hard-water effects in the aquatic plants that were dated and that radiocarbon ages of pollen may be anomalously old due to reworking. In their view, the luminescence ages are likely to be maximum...
Authors
Jeffrey Pigati, Kathleen Springer, Harrison J. Gray, Matthew Bennett, David Bustos
High-resolution geophysical and geochronological analysis of a relict shoreface deposit offshore central California: Implications for slip rate along the Hosgri fault High-resolution geophysical and geochronological analysis of a relict shoreface deposit offshore central California: Implications for slip rate along the Hosgri fault
The Cross-Hosgri slope is a bathymetric lineament that crosses the main strand of the Hosgri fault offshore Point Estero, central California. Recently collected chirp seismic reflection profiles and sediment cores provide the basis for a reassessment of Cross-Hosgri slope origin and the lateral slip rate of the Hosgri fault based on offset of the lower slope break of the Cross-Hosgri...
Authors
Jared W. Kluesner, Samuel Y. Johnson, Stuart P. Nishenko, Elisa Medri, Alex Simms, Gary Greene, Harrison J. Gray, Shannon Mahan, Jason Padgett, Emma Krolczyk, Daniel S. Brothers, James Conrad
Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: Examples from the western Sangre de Cristo Mountains, south-central Colorado Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: Examples from the western Sangre de Cristo Mountains, south-central Colorado
Debris-flow alluvial fans are iconic features of dynamic landscapes and are hypothesized to record tectonic and climatic change. Here, we highlight their complex formation and evolution through an exemplary suite of Quaternary debris-flow alluvial fans emanating from the western range front of the Sangre de Cristo Mountains in south-central Colorado, USA. To evaluate the constructive and...
Authors
Sylvia Nicovich, James Schmitt, Harrison J. Gray, Ralph Klinger, Shannon Mahan
Independent age estimates resolve the controversy of ancient human footprints at White Sands Independent age estimates resolve the controversy of ancient human footprints at White Sands
Human footprints at White Sands National Park, New Mexico, USA, reportedly date to between ~23,000 and 21,000 years ago according to radiocarbon dating of seeds from the aquatic plant Ruppia cirrhosa. These ages remain controversial because of potential old carbon reservoir effects that could compromise their accuracy. We present new calibrated 14C ages of terrestrial pollen collected...
Authors
Jeffrey Pigati, Kathleen Springer, Jeffrey Honke, David Wahl, Marie Champagne, Susan Zimmerman, Harrison J. Gray, Vincent Santucci, Daniel Odess, David Bustos, Matthew Bennett
Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition Paleohydrologic history of pluvial lake San Agustin, New Mexico: Tracking changing effective moisture in southwest North America through the last glacial transition
Paleoclimate records across the Intermountain West region of North America show significant regional variation in timing and magnitude of wet conditions that accompanied the last glacial-interglacial transition. To understand the climate controls on paleohydrologic change, well-dated records are needed across the region. The Plains of San Agustin (New Mexico, USA) is a closed-basin...
Authors
Adam Hudson, Jay Quade, Vance Holliday, Brendan Fenerty, Jordon Bright, Harrison Gray, Shannon Mahan
Luminescence sediment tracing reveals the complex dynamics of colluvial wedge formation Luminescence sediment tracing reveals the complex dynamics of colluvial wedge formation
Paleoearthquake studies that inform seismic hazard rely on assumptions of sediment transport that remain largely untested. Here, we test a widespread conceptual model and a new numerical model on the formation of colluvial wedges, a key deposit used to constrain the timing of paleoearthquakes. We perform this test by applying luminescence, a sunlight-sensitive sediment tracer, at a field...
Authors
Harrison J. Gray, Christopher DuRoss, Sylvia Nicovich, Ryan Gold
A geomorphic-process-based cellular automata model of colluvial wedge morphology and stratigraphy A geomorphic-process-based cellular automata model of colluvial wedge morphology and stratigraphy
The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding...
Authors
Harrison J. Gray, Christopher DuRoss, Sylvia Nicovich, Ryan Gold
How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)? How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)?
We excavated trenches at two paleoseismic sites bounding a trans-basin bedrock ridge (the Willow Creek Hills) along the northern Lost River fault zone to explore the uniqueness of the 1983 Mw 6.9 Borah Peak earthquake compared to its prehistoric predecessors. At the Sheep Creek site on the southernmost Warm Springs section, two earthquakes occurred at 9.8−14.0 ka (95% confidence) and 6.5...
Authors
Christopher DuRoss, Richard Briggs, Ryan Gold, Alexandra Hatem, Austin Elliott, Jaime Delano, Ivan Medina-Cascales, Harrison J. Gray, Shannon Mahan, Sylvia Nicovich, Zachery Lifton, Emily Kleber, Greg McDonald, Adam Hiscock, Mike Bunds, Nadine Reitman
Geologic Stories in Grand Canyon Geologic Stories in Grand Canyon
Take a trip through Grand Canyon with USGS geologists to learn about geologic mapping in this iconic landscape. On the trip, scientists from Arizona, New Mexico, California and Colorado also conducted a series of related research studies to inform the geologic maps and geologic history of Grand Canyon.
By
Core Science Systems Mission Area, Water Resources Mission Area, Environmental Health Program, National Cooperative Geologic Mapping Program, National Water Quality Program, Toxic Substances Hydrology, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center, New Mexico Water Science Center, Southwest Biological Science Center, Denver Radiogenic Isotope Lab, Mineralogy and Microscopy Laboratory, New Mexico Water Science Center Sediment Laboratory, Organic Geochemistry Laboratory, Geological Materials Repository, Geology and Ecology of National Parks, National Hydrography, Science Data Management, Colorado River Basin: Actionable and Strategic Integrated Science and Technology