Sam A Johnstone
(he/him)I am a Research Geologist interesested in understanding how processes of erosion and faulting interact to shape Earth’s surface. I study these phenomena through geologic maps, laboratory techniques that measure the history of rocks being exhumed toward the surface, and with measurements and models of Earth's surface topography.
I came to the USGS as a Mendenhall Postdoctoral Fellow in 2016 to study landscape evolution in the Southern Rocky Mountains and to help complete a facility for measuring the cooling histories of minerals as part of the Mineral Resources Program. In 2018 I transitioned to a job as a Research Geologist funded by the National Cooperative Geologic Mapping program, where I work now. In this capacity I conduct regional-scale geologic mapping and synthesis of Quaternary sedimentary deposits with the goal of ultimately establishing a seamlesss national-scale geologic map database that can aid in the characterization of geologic hazards and natural resources. This work is currently focused in two regions, in Arkansas and in a large transect spanning the Intermountain West, for which I also serve as the lead of the surficial geologic working group.
In addition to these roles I conduct research into the mechanisms of landscape evolution in an effort to better interpret the geologic record of natural hazards and past environmental change, focusing on two broad classifications of problems. First, I seek to develop numerical and statistical models to refine geologic inferences made from geochronologic data and to quantify uncertainty in those interpretations. Second, I try to understand the connection between earth surface processes, landscape form, and recent geologic deposits by developing numerical models that enable simulation of these phenomena. In these efforts I am interested in developing approaches for characterizing landscape evolution through paired analysis of topographic and geologic map data.
Prior to starting at the USGS I obtained my PhD from Stanford University in 2016, where I studied how sediment transport and erosion processes shaped hillslopes and river networks, and how some micro-climatic gradients enduced by aspect differences influenced these processes. In 2011 I obtained my MSc from UC Santa Cruz, where I had also obtained my BS a few years earlier. It was at UC Santa Cruz that I first got excited about geologic mapping and where I developed an interest in using low-temperature thermochronology to study histories of faulting.
Education and Certifications
Stanford University, PhD in Geology
UC Santa Cruz, MS in Geology
UC Santa Cruz, BS Earth Science
Science and Products
National Quaternary Geology
National Geologic Synthesis
Argon Geochronology
Ozark Dome-Arkoma Basin-Ouachita Transect
Geologic Framework of the Intermountain West
Surficial geologic map database for the Blanca Peak, Walsenburg, Trinidad, and Alamosa 30' x 60' quadrangles, Colorado
Datasets documenting late Pleistocene faulting in the Pondosa fault zone, Pit River Region, Northeastern California
Quaternary fault mapping of the Zapata and Blanca sections of the Sangre de Cristo fault zone from high-resolution 3DEP topography
Surficial geologic map database of the Aztec 1-degree by 2-degree quadrangle, northern New Mexico and southern Colorado: Contributions to the National Geologic Map
Surficial geologic map database of the Durango 1-degree by 2-degree quadrangle, southern Colorado: Contributions to the National Geologic Map
Detrital zircon geochronology and geochemistry data from the seafloor of the Bering Sea and adjacent river systems
Thermochronologic data from the southern Stillwater Range, Nevada
The National Cooperative Geologic Mapping Program’s U.S. GeoFramework Initiative — Delivering a digital database of geologic map information by 2030
The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS)
Mountain rivers reveal the earthquake hazard of geologic faults in Silicon Valley
Continental shelves as detrital mixers: U-Pb and Lu-Hf detrital zircon provenance of the Pleistocene–Holocene Bering Sea and its margins
Detrital signals of coastal erosion and fluvial sediment supply during glacio-eustatic sea-level rise, Southern California, USA
A Bayesian nonparametric approach to unmixing detrital geochronologic data
Detrital zircon record of magmatism and sediment dispersal across the North American Cordilleran arc system (28-48°N)
Identifying elusive piercing points along the North American transform margin using mixture modeling of detrital zircon data from sedimentary units and their crystalline sources
The grass is not always greener on the other side: Seasonal reversal of vegetation greenness in aspect-driven semiarid ecosystems
Timing of Cenozoic extension in the southern Stillwater Range and Dixie Valley, Nevada
Coexisting seismic behavior of transform faults revealed by high-resolution bathymetry
Dilution and propagation of provenance trends in sand and mud: Geochemistry and detrital zircon geochronology of modern sediment from central California (U.S.A.)
Non-USGS Publications**
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
dem_getter Python tool for acquiring digital elevation models and derivatives from The National Map
Science and Products
National Quaternary Geology
National Geologic Synthesis
Argon Geochronology
Ozark Dome-Arkoma Basin-Ouachita Transect
Geologic Framework of the Intermountain West
Surficial geologic map database for the Blanca Peak, Walsenburg, Trinidad, and Alamosa 30' x 60' quadrangles, Colorado
Datasets documenting late Pleistocene faulting in the Pondosa fault zone, Pit River Region, Northeastern California
Quaternary fault mapping of the Zapata and Blanca sections of the Sangre de Cristo fault zone from high-resolution 3DEP topography
Surficial geologic map database of the Aztec 1-degree by 2-degree quadrangle, northern New Mexico and southern Colorado: Contributions to the National Geologic Map
Surficial geologic map database of the Durango 1-degree by 2-degree quadrangle, southern Colorado: Contributions to the National Geologic Map
Detrital zircon geochronology and geochemistry data from the seafloor of the Bering Sea and adjacent river systems
Thermochronologic data from the southern Stillwater Range, Nevada
The National Cooperative Geologic Mapping Program’s U.S. GeoFramework Initiative — Delivering a digital database of geologic map information by 2030
The Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS)
Mountain rivers reveal the earthquake hazard of geologic faults in Silicon Valley
Continental shelves as detrital mixers: U-Pb and Lu-Hf detrital zircon provenance of the Pleistocene–Holocene Bering Sea and its margins
Detrital signals of coastal erosion and fluvial sediment supply during glacio-eustatic sea-level rise, Southern California, USA
A Bayesian nonparametric approach to unmixing detrital geochronologic data
Detrital zircon record of magmatism and sediment dispersal across the North American Cordilleran arc system (28-48°N)
Identifying elusive piercing points along the North American transform margin using mixture modeling of detrital zircon data from sedimentary units and their crystalline sources
The grass is not always greener on the other side: Seasonal reversal of vegetation greenness in aspect-driven semiarid ecosystems
Timing of Cenozoic extension in the southern Stillwater Range and Dixie Valley, Nevada
Coexisting seismic behavior of transform faults revealed by high-resolution bathymetry
Dilution and propagation of provenance trends in sand and mud: Geochemistry and detrital zircon geochronology of modern sediment from central California (U.S.A.)
Non-USGS Publications**
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.