Steven M. Cahan
Steven Cahan is a Cartographer with the USGS Geology, Energy & Minerals (GEM) Science Center in Reston, VA.
Steven received a bachelors degree in geography from Virginia Tech in 2010. Since joining the USGS, Steven has provided support in GIS to several projects including the CO2 sequestration project, the Gulf Coast assessment, and the National Geologic Map Database. His work includes geospatial analysis, map production, and keeping image servers up to date.
Professional Experience
May 2010 - present, Cartographer, USGS Geology, Energy & Minerals Science Center, Reston, VA
Education and Certifications
B.A. Geography - Geospatial and Environmental Analysis, Virginia Tech
Science and Products
Filter Total Items: 26
Spatial distribution of API gravity and gas/oil ratios for petroleum accumulations in Upper Cretaceous strata of the San Miguel, Olmos, and Escondido Formations of the south Texas Maverick Basin—Implications for petroleum migration and charge history
The Maverick Basin of south Texas is currently undergoing active exploration and production of gas and oil from tight sandstone reservoirs. The most productive tight sandstones in the basin are in the Upper Cretaceous San Miguel, Olmos, and Escondido Formations. These units are second only to the Eagle Ford Shale in terms of cumulative production volumes. The structural history of the...
Authors
Colin Doolan, William H. Craddock, Marc L. Buursink, Javin J. Hatcherian, Steven M. Cahan
Geologic carbon management options for the North Atlantic-Appalachian Region
IntroductionThe U.S. Geological Survey (USGS) North Atlantic-Appalachian Region is developing the regionwide capacity to provide timely science support for decision-makers attempting to enhance carbon removal, sequestration, and emissions mitigation to meet national atmospheric carbon reduction goals. The U.S. Environmental Protection Agency (EPA) reported that in 2021, the fourteen...
Authors
Peter D. Warwick, Madalyn Blondes, Sean T. Brennan, Steven M. Cahan, C. Özgen Karacan, Kevin Kroeger, Matthew D. Merrill
Assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources of the United States
In 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources that could be produced using current carbon dioxide enhanced oil recovery (CO2-EOR) technologies in amenable conventional oil reservoirs underlying onshore and State-owned offshore waters (herein after, onshore and State waters areas) of the conterminous...
Authors
Peter D. Warwick, E.D. Attanasi, Madalyn Blondes, Sean T. Brennan, Marc L. Buursink, Steven M. Cahan, Colin Doolan, Philip A. Freeman, C. Özgen Karacan, Celeste Lohr, Matthew D. Merrill, Ricardo A. Olea, Jenna Shelton, Ernie Slucher, Brian A. Varela
Dynamic estimates of geologic CO2 storage resources in the Illinois Basin constrained by reinjectivity of brine extracted for pressure management
Geologic carbon storage (GCS) is likely to be an important part of global efforts to decarbonize the energy industry. Widespread deployment of GCS relies on strategies to maximize CO2 injection rates while minimizing reservoir pressurization that could induce seismicity and/or fluid leakage into groundwater resources. Brine extraction from CO2 storage formations with subsurface...
Authors
Michelle R. Plampin, Steven T. Anderson, Steven M. Cahan, Stefan Finsterle
A novel method for conducting a geoenvironmental assessment of undiscovered ISR-amenable uranium Resources: Proof-of-concept in the Texas Coastal Plain
A geoenvironmental assessment methodology was developed to estimate waste quantities and disturbances that could be associated with the extraction of undiscovered uranium resources and identify areas on the landscape where uranium and other constituents of potential concern (COPCs) that may co-occur with uranium deposits in this region are likely to persist, if introduced into the...
Authors
Tanya Gallegos, Victoria G. Stengel, Katherine Walton-Day, Johanna Blake, Andrew Teeple, Delbert G Humberson, Steven M. Cahan, Douglas B. Yager, Kent Becher
Database of the "North America Tapestry of Time and Terrain" map
In 2000, the U.S. Geological Survey published a distinctive map, entitled “A Tapestry of Time and Terrain,” which showed a generalized depiction of the geology in the conterminous United States, draped over shaded-relief topography. In 2003, that map concept was extended geographically, and the resulting new map was published at 1:8,000,000 scale as “The North America Tapestry of Time...
Authors
Steven M. Cahan, Christopher Garrity, David R. Soller, José F. Vigil
National assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources — Summary
IntroductionIn 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources that might be produced by using current carbon dioxide enhanced oil recovery (CO2-EOR) technologies in amenable conventional oil reservoirs underlying the onshore and State waters areas of the conterminous United States. The assessment also...
Authors
Peter D. Warwick, E.D. Attanasi, Madalyn Blondes, Sean T. Brennan, Marc L. Buursink, Steven M. Cahan, Colin Doolan, Philip A. Freeman, C. Özgen Karacan, Celeste Lohr, Matthew D. Merrill, Ricardo A. Olea, Jenna Shelton, Ernie Slucher, Brian A. Varela
National assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources — Results
In 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources available if current carbon dioxide enhanced oil recovery (CO2-EOR) technologies were applied to amenable oil reservoirs underlying the onshore and State waters areas of the conterminous United States. The assessment also includes estimates of the mass of...
Authors
Peter D. Warwick, E.D. Attanasi, Madalyn Blondes, Sean T. Brennan, Marc L. Buursink, Steven M. Cahan, Colin Doolan, Philip A. Freeman, C. Özgen Karacan, Celeste Lohr, Matthew D. Merrill, Ricardo A. Olea, Jenna Shelton, Ernie Slucher, Brian A. Varela
Estimating market conditions for potential entry of new sources of anthropogenic CO2 for EOR in the Permian Basin
This study attempts to determine feasible carbon dioxide (CO2) price thresholds for entry of new sources of anthropogenic (man-made) CO2 for utilization in enhanced oil recovery (EOR) in the Permian Basin. Much of the discussion about carbon capture, utilization, and storage (CCUS) has focused on the high costs of carbon capture as the major barrier to entry of new anthropogenic sources...
Authors
Steven T. Anderson, Steven M. Cahan
Geologic framework for the national assessment of carbon dioxide storage resources—Atlantic Coastal Plain and Eastern Mesozoic Rift Basins
This chapter presents information pertinent to the geologic carbon dioxide (CO2) sequestration potential within saline aquifers located in the Atlantic Coastal Plain and Eastern Mesozoic Rift Basins of the Eastern United States. The Atlantic Coastal Plain is underlain by a Jurassic to Quaternary succession of sedimentary strata that onlap westward onto strata of the Appalachian Piedmont...
Authors
William H. Craddock, Matthew D. Merrill, Tina L. Roberts-Ashby, Sean T. Brennan, Marc L. Buursink, Ronald M. Drake, Peter D. Warwick, Steven M. Cahan, Christina A. DeVera, Philip A. Freeman, Mayur A. Gosai, Celeste Lohr
Geologic assessment of undiscovered oil and gas resources—Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups, United States Gulf of Mexico Coastal Plain and State Waters
In 2010, the U.S. Geological Survey (USGS) assessed Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups and their equivalent units for technically recoverable, undiscovered hydrocarbon resources underlying onshore lands and State Waters of the Gulf Coast region of the United States. This assessment was based on a geologic model...
Authors
Sharon M. Swanson, Catherine B. Enomoto, Kristin Opferkuch Dennen, Brett Valentine, Steven M. Cahan
Geologic framework for the national assessment of carbon dioxide storage resources—Southern Rocky Mountain Basins: Chapter M in Geologic framework for the national assessment of carbon dioxide storage resources
The U.S. Geological Survey has completed an assessment of the potential geologic carbon dioxide storage resources in the onshore areas of the United States. To provide geological context and input data sources for the resources numbers, framework documents are being prepared for all areas that were investigated as part of the national assessment. This report, chapter M, is the geologic...
Authors
Matthew D. Merrill, Ronald M. Drake, Marc L. Buursink, William H. Craddock, Joseph A. East, Ernie Slucher, Peter D. Warwick, Sean T. Brennan, Madalyn Blondes, Philip A. Freeman, Steven M. Cahan, Christina A. DeVera, Celeste Lohr
Carbon Dioxide Storage Resources - California Basins: Chapter Q, Spatial Data
This data release provides shapefiles that represent storage assessment units (SAUs) and drilling-density cells in the Central California Coast, Los Angeles, Sacramento, San Joaquin, and Ventura Basins of California in the United States. The SAU is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2...
Data associated with using lidar and earth observation temporal analysis to explore and characterize uranium mining on the south Texas landscape
Open pit uranium mining in Atascosa, Karnes, and Live Oak Counties in the Texas gulf coast region was active during the second half of the 20th century. Understanding the history of these mining operations is important for proper management and restoration. Although some mines have extensive records documenting the locations and extents of mining pits and mine waste-rock piles, and...
Carbon Dioxide Storage Resources-Anadarko and Southern Oklahoma Basins: Chapter R. Spatial Data
This data release provides shapefiles that represent storage assessment units (SAUs) and drilling-density cells in the Anadarko and Southern Oklahoma Basins of Colorado, Kansas, Oklahoma, and Texas in the United States. The SAU is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2 storage resources...
Carbon Dioxide Storage Resources - Appalachian Basin, Black Warrior Basin, Illinois Basin, and Michigan Basin: Chapter P, Spatial Data
The storage assessment unit (SAU) is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2 storage resources. The SAU is shown here as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the assessment interval. Individual SAUs are defined on the basis of common...
Carbon Dioxide Storage Resources-Wind River Basin: Chapter O, Spatial Data
The storage assessment unit (SAU) is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2 storage resources. The SAU is shown here as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the assessment interval. Individual SAUs are defined on the basis of common...
Optimization simulations to estimate maximum brine injection rates in the Illinois Basin
We developed a methodology to estimate maximum brine injection rates in subsurface formations across wide geographic areas using inverse modeling-based optimization techniques. We first defined geographic areas where groundwater was too saline to meet the standard for drinking water and where sufficient confining units existed above and below the injection layers. We then assumed...
National assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources - data release
In 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources available if current carbon dioxide enhanced oil recovery (CO2-EOR) technologies were applied in amenable oil reservoirs underlying the onshore and State waters area of the conterminous United States. The assessment also includes estimates of the...
Geologic formations and mine locations for potential CO2 mineralization
This geodatabase contains geologic unit boundaries and asbestos site locations shown in "Carbon dioxide mineralization feasibility in the United States" (Blondes and others, 2019). Data was compiled from source material at a scale range of 1:100,000 to 1:5,000,000 and is not intended for any greater detail.
USGS Gulf Coast Source Rock Database (ver. 2.0, October 2023)
The USGS Gulf Coast Source Rock Database (GCSRD) is an online repository for all publicly available source rock data (outcrop and subsurface) from the states of Florida, Georgia, Alabama, Mississippi, Louisiana, Arkansas, and Texas. "Source rock data" are defined in this context as data that include any of the following measured or calculated parameters: -total organic carbon (TOC),...
USGS Gulf Coast Petroleum Systems, and National and Global Oil and Gas Assessment Projects - U.S. Gulf Coast Downdip Paleogene Formations 2017 Assessment Unit Boundaries and Input-Data Forms
The Assessment Unit is the fundamental unit used in the National Assessment Project for the assessment of undiscovered oil and gas resources. The Assessment Unit is defined within the context of the higher-level Total Petroleum System. The Assessment Unit is shown herein as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the province and...
Science and Products
Filter Total Items: 26
Spatial distribution of API gravity and gas/oil ratios for petroleum accumulations in Upper Cretaceous strata of the San Miguel, Olmos, and Escondido Formations of the south Texas Maverick Basin—Implications for petroleum migration and charge history
The Maverick Basin of south Texas is currently undergoing active exploration and production of gas and oil from tight sandstone reservoirs. The most productive tight sandstones in the basin are in the Upper Cretaceous San Miguel, Olmos, and Escondido Formations. These units are second only to the Eagle Ford Shale in terms of cumulative production volumes. The structural history of the...
Authors
Colin Doolan, William H. Craddock, Marc L. Buursink, Javin J. Hatcherian, Steven M. Cahan
Geologic carbon management options for the North Atlantic-Appalachian Region
IntroductionThe U.S. Geological Survey (USGS) North Atlantic-Appalachian Region is developing the regionwide capacity to provide timely science support for decision-makers attempting to enhance carbon removal, sequestration, and emissions mitigation to meet national atmospheric carbon reduction goals. The U.S. Environmental Protection Agency (EPA) reported that in 2021, the fourteen...
Authors
Peter D. Warwick, Madalyn Blondes, Sean T. Brennan, Steven M. Cahan, C. Özgen Karacan, Kevin Kroeger, Matthew D. Merrill
Assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources of the United States
In 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources that could be produced using current carbon dioxide enhanced oil recovery (CO2-EOR) technologies in amenable conventional oil reservoirs underlying onshore and State-owned offshore waters (herein after, onshore and State waters areas) of the conterminous...
Authors
Peter D. Warwick, E.D. Attanasi, Madalyn Blondes, Sean T. Brennan, Marc L. Buursink, Steven M. Cahan, Colin Doolan, Philip A. Freeman, C. Özgen Karacan, Celeste Lohr, Matthew D. Merrill, Ricardo A. Olea, Jenna Shelton, Ernie Slucher, Brian A. Varela
Dynamic estimates of geologic CO2 storage resources in the Illinois Basin constrained by reinjectivity of brine extracted for pressure management
Geologic carbon storage (GCS) is likely to be an important part of global efforts to decarbonize the energy industry. Widespread deployment of GCS relies on strategies to maximize CO2 injection rates while minimizing reservoir pressurization that could induce seismicity and/or fluid leakage into groundwater resources. Brine extraction from CO2 storage formations with subsurface...
Authors
Michelle R. Plampin, Steven T. Anderson, Steven M. Cahan, Stefan Finsterle
A novel method for conducting a geoenvironmental assessment of undiscovered ISR-amenable uranium Resources: Proof-of-concept in the Texas Coastal Plain
A geoenvironmental assessment methodology was developed to estimate waste quantities and disturbances that could be associated with the extraction of undiscovered uranium resources and identify areas on the landscape where uranium and other constituents of potential concern (COPCs) that may co-occur with uranium deposits in this region are likely to persist, if introduced into the...
Authors
Tanya Gallegos, Victoria G. Stengel, Katherine Walton-Day, Johanna Blake, Andrew Teeple, Delbert G Humberson, Steven M. Cahan, Douglas B. Yager, Kent Becher
Database of the "North America Tapestry of Time and Terrain" map
In 2000, the U.S. Geological Survey published a distinctive map, entitled “A Tapestry of Time and Terrain,” which showed a generalized depiction of the geology in the conterminous United States, draped over shaded-relief topography. In 2003, that map concept was extended geographically, and the resulting new map was published at 1:8,000,000 scale as “The North America Tapestry of Time...
Authors
Steven M. Cahan, Christopher Garrity, David R. Soller, José F. Vigil
National assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources — Summary
IntroductionIn 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources that might be produced by using current carbon dioxide enhanced oil recovery (CO2-EOR) technologies in amenable conventional oil reservoirs underlying the onshore and State waters areas of the conterminous United States. The assessment also...
Authors
Peter D. Warwick, E.D. Attanasi, Madalyn Blondes, Sean T. Brennan, Marc L. Buursink, Steven M. Cahan, Colin Doolan, Philip A. Freeman, C. Özgen Karacan, Celeste Lohr, Matthew D. Merrill, Ricardo A. Olea, Jenna Shelton, Ernie Slucher, Brian A. Varela
National assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources — Results
In 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources available if current carbon dioxide enhanced oil recovery (CO2-EOR) technologies were applied to amenable oil reservoirs underlying the onshore and State waters areas of the conterminous United States. The assessment also includes estimates of the mass of...
Authors
Peter D. Warwick, E.D. Attanasi, Madalyn Blondes, Sean T. Brennan, Marc L. Buursink, Steven M. Cahan, Colin Doolan, Philip A. Freeman, C. Özgen Karacan, Celeste Lohr, Matthew D. Merrill, Ricardo A. Olea, Jenna Shelton, Ernie Slucher, Brian A. Varela
Estimating market conditions for potential entry of new sources of anthropogenic CO2 for EOR in the Permian Basin
This study attempts to determine feasible carbon dioxide (CO2) price thresholds for entry of new sources of anthropogenic (man-made) CO2 for utilization in enhanced oil recovery (EOR) in the Permian Basin. Much of the discussion about carbon capture, utilization, and storage (CCUS) has focused on the high costs of carbon capture as the major barrier to entry of new anthropogenic sources...
Authors
Steven T. Anderson, Steven M. Cahan
Geologic framework for the national assessment of carbon dioxide storage resources—Atlantic Coastal Plain and Eastern Mesozoic Rift Basins
This chapter presents information pertinent to the geologic carbon dioxide (CO2) sequestration potential within saline aquifers located in the Atlantic Coastal Plain and Eastern Mesozoic Rift Basins of the Eastern United States. The Atlantic Coastal Plain is underlain by a Jurassic to Quaternary succession of sedimentary strata that onlap westward onto strata of the Appalachian Piedmont...
Authors
William H. Craddock, Matthew D. Merrill, Tina L. Roberts-Ashby, Sean T. Brennan, Marc L. Buursink, Ronald M. Drake, Peter D. Warwick, Steven M. Cahan, Christina A. DeVera, Philip A. Freeman, Mayur A. Gosai, Celeste Lohr
Geologic assessment of undiscovered oil and gas resources—Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups, United States Gulf of Mexico Coastal Plain and State Waters
In 2010, the U.S. Geological Survey (USGS) assessed Lower Cretaceous Albian to Upper Cretaceous Cenomanian carbonate rocks of the Fredericksburg and Washita Groups and their equivalent units for technically recoverable, undiscovered hydrocarbon resources underlying onshore lands and State Waters of the Gulf Coast region of the United States. This assessment was based on a geologic model...
Authors
Sharon M. Swanson, Catherine B. Enomoto, Kristin Opferkuch Dennen, Brett Valentine, Steven M. Cahan
Geologic framework for the national assessment of carbon dioxide storage resources—Southern Rocky Mountain Basins: Chapter M in Geologic framework for the national assessment of carbon dioxide storage resources
The U.S. Geological Survey has completed an assessment of the potential geologic carbon dioxide storage resources in the onshore areas of the United States. To provide geological context and input data sources for the resources numbers, framework documents are being prepared for all areas that were investigated as part of the national assessment. This report, chapter M, is the geologic...
Authors
Matthew D. Merrill, Ronald M. Drake, Marc L. Buursink, William H. Craddock, Joseph A. East, Ernie Slucher, Peter D. Warwick, Sean T. Brennan, Madalyn Blondes, Philip A. Freeman, Steven M. Cahan, Christina A. DeVera, Celeste Lohr
Carbon Dioxide Storage Resources - California Basins: Chapter Q, Spatial Data
This data release provides shapefiles that represent storage assessment units (SAUs) and drilling-density cells in the Central California Coast, Los Angeles, Sacramento, San Joaquin, and Ventura Basins of California in the United States. The SAU is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2...
Data associated with using lidar and earth observation temporal analysis to explore and characterize uranium mining on the south Texas landscape
Open pit uranium mining in Atascosa, Karnes, and Live Oak Counties in the Texas gulf coast region was active during the second half of the 20th century. Understanding the history of these mining operations is important for proper management and restoration. Although some mines have extensive records documenting the locations and extents of mining pits and mine waste-rock piles, and...
Carbon Dioxide Storage Resources-Anadarko and Southern Oklahoma Basins: Chapter R. Spatial Data
This data release provides shapefiles that represent storage assessment units (SAUs) and drilling-density cells in the Anadarko and Southern Oklahoma Basins of Colorado, Kansas, Oklahoma, and Texas in the United States. The SAU is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2 storage resources...
Carbon Dioxide Storage Resources - Appalachian Basin, Black Warrior Basin, Illinois Basin, and Michigan Basin: Chapter P, Spatial Data
The storage assessment unit (SAU) is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2 storage resources. The SAU is shown here as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the assessment interval. Individual SAUs are defined on the basis of common...
Carbon Dioxide Storage Resources-Wind River Basin: Chapter O, Spatial Data
The storage assessment unit (SAU) is the fundamental unit used in the National Assessment of Geologic Carbon Dioxide Storage Resources project for the assessment of geologic CO2 storage resources. The SAU is shown here as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the assessment interval. Individual SAUs are defined on the basis of common...
Optimization simulations to estimate maximum brine injection rates in the Illinois Basin
We developed a methodology to estimate maximum brine injection rates in subsurface formations across wide geographic areas using inverse modeling-based optimization techniques. We first defined geographic areas where groundwater was too saline to meet the standard for drinking water and where sufficient confining units existed above and below the injection layers. We then assumed...
National assessment of carbon dioxide enhanced oil recovery and associated carbon dioxide retention resources - data release
In 2020, the U.S. Geological Survey (USGS) completed a probabilistic assessment of the volume of technically recoverable oil resources available if current carbon dioxide enhanced oil recovery (CO2-EOR) technologies were applied in amenable oil reservoirs underlying the onshore and State waters area of the conterminous United States. The assessment also includes estimates of the...
Geologic formations and mine locations for potential CO2 mineralization
This geodatabase contains geologic unit boundaries and asbestos site locations shown in "Carbon dioxide mineralization feasibility in the United States" (Blondes and others, 2019). Data was compiled from source material at a scale range of 1:100,000 to 1:5,000,000 and is not intended for any greater detail.
USGS Gulf Coast Source Rock Database (ver. 2.0, October 2023)
The USGS Gulf Coast Source Rock Database (GCSRD) is an online repository for all publicly available source rock data (outcrop and subsurface) from the states of Florida, Georgia, Alabama, Mississippi, Louisiana, Arkansas, and Texas. "Source rock data" are defined in this context as data that include any of the following measured or calculated parameters: -total organic carbon (TOC),...
USGS Gulf Coast Petroleum Systems, and National and Global Oil and Gas Assessment Projects - U.S. Gulf Coast Downdip Paleogene Formations 2017 Assessment Unit Boundaries and Input-Data Forms
The Assessment Unit is the fundamental unit used in the National Assessment Project for the assessment of undiscovered oil and gas resources. The Assessment Unit is defined within the context of the higher-level Total Petroleum System. The Assessment Unit is shown herein as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the province and...