Preliminary geology of the McGrath - upper Innoko River area, western interior Alaska

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What does this data set describe?

Title:
Preliminary geology of the McGrath - upper Innoko River area, western interior Alaska
Abstract:
Preliminary geology of the McGrath - upper Innoko River area, western interior Alaska, Alaska Open-File Report 134, presents results of geologic mapping and resource assessment across approximately 900 square miles in parts of the McGrath, Iditarod, and Ophir 1:250,000 quadrangles of western interior Alaska. DGGS staff completed a total of ninety-four field days in 1972, 1978, and 1979. The map area contains a Late Paleozoic chert-argillite-limestone unit, Early(?) Cretaceous limy sandstone and impure limestone, and a thick section of mid- to Late Cretaceous lithic sandstone, siltstone, shale, and conglomerate. Layered sedimentary rocks form low, rounded ridges, and igneous complexes and associated hornfels form steep massifs. Bedrock exposures are limited below timberline but are well developed along stream bluffs and in the Beaver Mountains. Late Cretaceous alkaline plutonic complexes, dike swarms, and associated mafic volcanic rocks intrude and overlie the layered units. Surficial deposits include glacial, eolian, alluvial, and colluvial sediments. Dominant structures consist of northeast-trending folds and high-angle faults. Placer gold deposits occur in modern and older stream terraces in the Ophir mining area and the Candle Hills. Gold placers are associated with basaltic-to-rhyolitic dike swarms and faults that cross stream channels. The dike swarms contain anomalous concentrations of gold, nickel, yttrium, chromium, and zirconium, and fractures in plutons and nearby hornfels zones locally contain anomalous base and precious metals interpreted as probable lode sources for gold placers in the Candle Hills. The geologic relationships recorded by this map have important implications for understanding mineral resources and guiding future exploration throughout this region of Alaska. The dataset provides geologic, structural, stratigraphic, and geochronologic information organized according to the GeMS and AK GeMS mapping schemas. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: https://doi.org/10.14509/53.
Supplemental_Information:
This geodatabase is organized according to the AK GeMS mapping schema Hendricks, M.D., Macpherson, A.E., Athey, J.E., Wyatt, W.C., Montayne, Simone, Buchanan, Wes, Rivera, P.G., and Steinleitner, A.M., 2024, AK GeMS data dictionary: A description of the Alaska geologic mapping schema: Alaska Division of Geological & Geophysical Surveys Miscellaneous Publication 170 v. 2, 13 p. https://doi.org/10.14509/31172. The distribution package includes ESRI fonts and style files, along with usage instructions. Further documentation of the symbology is provided by Ekberg, P.G., Hendricks, M.D., and Athey, J.E., 2021, AK GeMS symbology: A description of the AK GeMS style file: Alaska Division of Geological & Geophysical Surveys Miscellaneous Publication 169, 7 p. https://doi.org/10.14509/30584.
  1. How might this data set be cited?
    Bundtzen, T.K., and Laird, G.M., 1980, Preliminary geology of the McGrath - upper Innoko River area, western interior Alaska: Alaska Open-File Report AOF 134, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 39 p., 2 sheets
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -157.182321
    East_Bounding_Coordinate: -155.504112
    North_Bounding_Coordinate: 63.175279
    South_Bounding_Coordinate: 62.719700
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 1972
    Ending_Date: 1979
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: geodatabase
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a vector data set.
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 4
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -159
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.000000
      False_Northing: 0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest .00000001
      Ordinates (y-coordinates) are specified to the nearest .00000001
      Planar coordinates are specified in Meters
      The horizontal datum used is NAD27.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.9786982.
  7. How does the data set describe geographic features?
    mcgrath_upper_innoko_river_ak_gems_db
    Geodatabase, layer files, style files, and fonts (Source: DGGS)
    mcgrath_upper_innoko_river_gems_db
    Geodatabase, layer files, style files, and fonts (Source: DGGS)
    mcgrath_upper_innoko_river_gems_geopackage
    SQLite Database file (Source: DGGS)
    mcgrath_upper_innoko_river_gems_shapefile
    Shapefiles and open data files (Source: DGGS)

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    Thomas K. Bundtzen led the project and was assisted by Gregory M. Laird during all three seasons, and by Virginia F. Ferrell, Nicki D. Coursey, and Karen S. Emmel in 1979. Specialists contributed fossil locality data, paleocurrent measurements, K-Ar age determinations, geochemical analyses, gold production figures, and uranium and thorium analyses. Additional geological comparisons were provided by U.S. Geological Survey staff familiar with nearby quadrangles. Long-time local residents shared information on past mineral activity, and the Rossander mining camp on Yankee Creek served as the 1979 base camp. The report was reviewed by DGGS staff. This map was converted to GeMS or digitized into GeMS by Kinney Engineering, LCC., quality controlled, and then finalized by DGGS staff (Chris Wyatt and Mike Hendricks). Ally M. Steinleitner implemented final database quality control and packaging. This geologic map (or report or conversion or product, etc.) was funded by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G24AC00521, 2024, and the State of Alaska General Fund. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.

Why was the data set created?

This report provides geologic mapping and resource information for parts of the McGrath, Iditarod, and Ophir 1:250,000 quadrangles of western interior Alaska. The mapping improves understanding of bedrock geology, surficial deposits, and structural features, and documents the distribution and geologic controls of placer gold deposits in the Ophir mining precinct and Candle Hills. These data support mineral resource evaluation, land management, and future geologic investigations in the region.

How was the data set created?

  1. From what previous works were the data drawn?
    Ekberg, P.G. and others, 2021 (source 1 of 3)
    Ekberg, P.G., Hendricks, M.D., and Athey, J.E., 2021, AK GeMS symbology: A description of the AK GeMS style file: Miscellaneous Publication MP 169, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 7 p
    Type_of_Source_Media: paper
    Source_Contribution: GIS analysis and digital cartography
    Hendricks, M.D. and others, 2021 (source 2 of 3)
    Hendricks, M.D., Ekberg, P.G., Athey, J.E., Wyatt, W.C., Willingham, A.L., and Naibert, T.J., 2021, AK GeMS data dictionary: A description of the Alaska geologic mapping schema: Miscellaneous Publication MP 170, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 10 p
    Type_of_Source_Media: paper
    Source_Contribution: GIS analysis and digital cartography
    U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020 (source 3 of 3)
    U.S. Geological Survey National Cooperative Geologic Mapping Program, 2020, GeMS (Geologic Map Schema) - A standard format for the digital publication of geologic maps: Techniques and Methods TM 11-B10, U.S. Geological Survey, United States.

    Online Links:

    Other_Citation_Details: 1 p
    Type_of_Source_Media: paper
    Source_Contribution: GIS analysis and digital cartography
  2. How were the data generated, processed, and modified?
    Date: 1979 (process 1 of 2)
    Geologic mapping - DGGS completed geologic mapping during ninety-four field days in 1972, 1978, and 1979. Mapping documented bedrock lithologies, intrusive and volcanic relationships, structural features, and surficial deposits across parts of the McGrath, Iditarod, and Ophir quadrangles. Field investigations included measurement of paleocurrent indicators, identification of fossil localities, and collection of rock and sediment samples for geochemical and age-dating analyses. Supporting data included fossil identifications, K-Ar age determinations, and uranium and thorium analyses. Information on historical mineral activity was gathered from local residents, and geological comparisons with nearby quadrangles were incorporated into final interpretations.
    Date: 2026 (process 2 of 2)
    Data packaging - DGGS organized and attributed the geologic and geographic features according to the AK GeMS schema, then programmatically transformed the data into four distribution formats: (1) an AK GeMS data package containing the full database and supporting files, (2) a GeMS data package converted to the USGS base standard, (3) a SQLite database file, and (4) a simplified shapefile package with shapefile representations of the data.
  3. What similar or related data should the user be aware of?
    Bundtzen, T.K., and Laird, G.M., 1982, Geologic map of the Iditarod D-2 and eastern D-3 quadrangles, Alaska: Geologic Report GR 72, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Bundtzen, T.K., and Laird, G.M., 1983, Geologic map of the Iditarod D-1 Quadrangle, Alaska: Professional Report PR 78, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Bundtzen, T.K., and Laird, G.M., 1983, Geologic map of the McGrath D-6 Quadrangle, Alaska: Professional Report PR 79, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Bundtzen, T.K., and Laird, G.M., 1983, Preliminary geology of the northeastern Iditarod C-3 Quadrangle, Alaska: Report of Investigation RI 83-13, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:63,360
    Bundtzen, T.K., Laird, G.M., and Lockwood, M.S., 1988, Geologic map of the Iditarod C-3 Quadrangle, Alaska: Professional Report PR 96, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 13 p., 1 sheet, scale 1:63,360
    Burns, L.E., Graham, G.R.C., Barefoot, J.D., Naibert, T.J., and Fugro Airborne Surveys Corp., 2019, Iditarod electromagnetic and magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2019-15, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 15 p
    Burns, L.E., Graham, G.R.C., Barefoot, J.D., Naibert, T.J., CGG, and Fugro Airborne Surveys Corp., 2019, Fox Hills electromagnetic and magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2018-6, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 14 p
    Fusso, L.A., Petersen, E.I., Emond, A.M., and Inc., EON Geosciences, 2026, Kuskokwim airborne magnetic and radiometric geophysical survey, Ganes Creek, Alaska (2026): Geophysical Report GPR 2026-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 16 p
    Fusso, L.A., Petersen, E.I., Emond, A.M., and Inc., EON Geosciences, 2026, Kuskokwim airborne magnetics and radiometric geophysical survey, McGrath, Alaska: Geophysical Report GPR 2026-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 17 p
    Meyer, J.F., and Krouskop, D.L., 1986, Preliminary gravity data of the Minchumina basin, southcentral Alaska: Report of Investigation RI 86-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 14 p., 2 sheets, scale 1:500,000
    Petersen, E.I., Fusso, L.A., Ltd., Geotech, and Frameworks, Aqua Geo LLC, 2026, Candle Hills airborne electromagnetic survey, Kuskokwim region, Alaska: Geophysical Report GPR 2026-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 9 p
    Reger, R.D., Campbell, K.M., Stevens, D.S.P., and Smith, R.L., 2003, Survey of geology, geologic materials, and geologic hazards in proposed access corridors in the Ophir Quadrangle, Alaska: Miscellaneous Publication MP 100, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 5 sheets, scale 1:250,000
    Reger, R.D., Cruse, G.R., Stevens, D.S.P., and Smith, R.L., 2003, Survey of geology, geologic materials, and geologic hazards in proposed access corridors in the Iditarod Quadrangle, Alaska: Miscellaneous Publication MP 76, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 4 sheets, scale 1:250,000
    Reger, R.D., Stevens, D.S.P., Cruse, G.R., and Livingston, H.R., 2003, Survey of geology, geologic materials, and geologic hazards in proposed access corridors in selected quadrangles, Alaska: Miscellaneous Publication MP 129, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 72 p

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    Attribute fields within each feature class are populated using the map symbology and corresponding applicable values from the GeMS and AK GeMS specifications. When known, certainty in attribute interpretation is indicated in the relevant fields. Attribute accuracy varies throughout the map and is scale-dependent.
  2. How accurate are the geographic locations?
    Certainty in feature boundaries or location varies throughout the map. Data fields within each feature class and the accompanying orientation and location confidence lookup tables record the authors' degree of confidence in the location of applicable features.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This publication is a DGGS Alaska Open-File Report (AOF). An AOF contains reports of research by DGGS personnel. Its objective was to make information available to the public as soon as possible, and therefore reports of this series were not subjected to rigorous critical review and formal editing and did not use professional cartographic services.
  5. How consistent are the relationships among the observations, including topology?
    All polygon features were topologically validated according to the AK GeMS geologic mapping schema specifications.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
  1. Who distributes the data set? (Distributor 1 of 1)
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set? AOF 134
  3. What legal disclaimers am I supposed to read?
    The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 30-Jul-2026
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK
USA

(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov
Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.50 on Thu Jul 30 16:01:31 2026