Geologic map of the Iditarod D-2 and eastern D-3 quadrangles, Alaska, Geologic Report 72, provides 1:63,360-scale geologic mapping of the Beaver Mountains and the surrounding area within the Kuskokwim Mountains uplands. This work was part of a series of reports on the geology, geochemistry, and mineral resources of the Iditarod quadrangle, Alaska. This publication also includes detailed geologic, structural, stratigraphic, and geochronologic data. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: http://doi.org/10.14509/432.

The Mineral Resources section of the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted 500 mi2 of 1:63,360-scale geologic mapping in the northeastern Tanacross Quadrangle (Tanacross D-1, and parts of the C-1, C-2, and D-2 quadrangles), located 15 miles southeast of Chicken, Alaska. The project took place during two periods: a reconnaissance mapping effort June 12-22, 2017, and a detailed campaign from June 18 to July 16, 2018. This map is located within an area of current industry interest; it includes the Taurus porphyry copper-gold-molybdenum +/- rhenium deposit and several other occurrence types, including gold, copper, and molybdenum in porphyritic intrusions, structurally controlled silver-lead-zinc prospects, and placer gold deposits. This map includes unconsolidated surficial deposits in the Tanacross D-1 Quadrangle, the eastern one-third of the Tanacross D-2 Quadrangle, the northern half of the Tanacross B-2 Quadrangle and the northeastern one-third of the Tanacross B-2 Quadrangle. Surficial geology was primarily mapped by interpreting 2.5-m-resolution SPOT 5 color-infrared and natural color red-green-blue (RGB) imagery collected in 2009 and 2010 and stereoscopic pairs of approximately 1:65,000-scale, false-color, infrared aerial photographs taken in 1978 and 1981. Surficial mapping was augmented with helicopter-supported fieldwork June 20-23, 2017 and July 3-4, 2018 to visit exposures and check geologic mapping. The complete report and digital data are available from the DGGS website: http://doi.org/10.14509/30197.

Surficial-geologic map of the Seward D-6 Quadrangle, Alaska, Report of Investigation 84-15, shows the distribution of unconsolidated deposits and undifferentiated bedrock around the eastern apex of the Turnagain Arm, in South Central Alaska. This map was prepared principally by interpreting 1:60,000 false-color, infrared aerial photographs taken in 1978 and locally verified by ground observations. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: http://doi.org/10.14509/2374.

Scientific Investigations Map 2975, Geologic map of the Big Delta B-1 Quadrangle, east-central Alaska, provides detailed (1:63,360-scale) geologic mapping of the U.S. Geological Survey (USGS) Big Delta B-1 quadrangle. This data release is a conversion of the originating geospatial data published by the USGS and may include minor modifications necessary for schema compliance. The dataset contains geologic, structural, stratigraphic, and geochronologic data organized according to the GeMS and AK GeMS mapping schemas. The geodatabase and ESRI fonts and style files are available from the DGGS website: https://dggs.alaska.gov/pubs/id/23531.

This map is a compilation of previously unpublished and published data, as well as from updated field mapping. This publication offers a 1:125,000-scale map sheet accompanied by a booklet containing a summary of the geology, a colored terrane map, map unit descriptions, a summary table listing selected mineral deposits and energy resources, references, and a correlation of map units. The text (in the report) describes the geology and resource potential of a highly mineralized region centered in the Farewell silver-lead-zinc district southeast of McGrath. Potentially important coal resources flanking the Alaska Range are also described in the map area.

Report of Investigation 2018-6, Geologic map of the Umiat-Gubik area, central North Slope, Alaska, provides a 1:63,360-scale geologic map of the hydrocarbon-bearing Umiat-Gubik area of the central North Slope, Alaska, spans approximately 2,100 km2 at the northern extent of the Brooks Range foothills fold-and-thrust belt in the Colville foreland basin. This geologic map was prepared through assimilation of field observations, aerial and satellite imagery, seismic-reflection data, and well logs. Near-surface formation picks were available or derived for most of the area's 24 exploration wells, and two cross-sections were constructed along lines of section that are constrained at depth by our interpretations of publicly available two-dimensional seismic data. The mapped area hosts exposures of Upper Cretaceous strata in the Nanushuk, Seabee, Tuluvak, Schrader Bluff, and Prince Creek Formations, constituting an approximately 2-km-thick succession that crops out discontinuously in the low-relief, tundra-mantled region. This part of the siliciclastic Brookian megasequence stratigraphy comprises principally shallow-marine deposits. Our work benefits from and reflects recent sequence-stratigraphic advances that better constrain how this part of the Colville basin continued to fill by a northeastward prograding clastic wedge during Late Cretaceous time, with the exposed stratigraphy recognized as basin-scale topset units. A series of east- to east-southeast-trending, km-scale wavelength, gentle folds are mapped in the area. Anticlines are locally breached by thrusts and interpreted to be folded above faulted and penetratively deformed mid-Cretaceous Torok Formation. Undeveloped, sub-commercial (as of this writing) petroleum accumulations occur along doubly plunging anticlinal traps at three long-recognized fields in the map area: Umiat (mostly oil), Gubik (gas), and East Umiat (gas). The Umiat oil field structural culmination is modified by thrust faults that breach the surface, and the East Umiat gas field is associated with a north-dipping back-thrust that is evident in seismic data and cuts across the Upper Cretaceous stratigraphy; thrust faults near the Gubik gas field lie within and below the Torok Formation. Various interpretations have previously been published for some of the area's structures, with important implications for petroleum trap geometries in the gas-prone foothills region. We present new data and interpretations that support the inference of a principal, south-dipping thrust fault that breaches the north limb of Umiat anticline near Umiat. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: http://doi.org/10.14509/30099.

Preliminary geologic map of parts of the Anchorage C-2, C-3, D-2, and D-3 quadrangles, Alaska, Report of Investigation 83-10,RI 83-10 presents 1:25,000-scale geologic mapping of the north-central Chugach Mountains. This rugged area, approximately 120 km NE of Anchorage, straddles the Matanuska Glacier and includes rocks of the southern (lower) Peninsular Terrane and northern Chugach Terrane. Helicopter-supported field work lasted 4-8 weeks each summer during 1980-1982. Most of the previous mapping in the area was at 1:250,000-scale, and this work provides a much more detailed examination of rock types and structures in the area. In particular, the contact between Peninsular and Chugach Terranes (Border Ranges Fault) is present as a complex series of mostly steeply-dipping faults, commonly with ambiguous units separating the two. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: http://doi.org/10.14509/2349.

Geologic map of the Iditarod D-1 Quadrangle, Alaska, Professional Report 78, provides 1:63,360-scale geologic mapping of parts of McGrath and Innoko mining districts in Kuskokwim Mountains uplands. Paleozoic and Cretaceous sedimentary and volcanic rocks dominate the region's geology, and the Nixon-Iditarod and the Yankee-Ganes Creek faults bisect it. Significant rock units were also studied in the laboratory using standard thin section (transmitted light) petrographic techniques, fossil identifications, multi-element and major-oxide geochemical analyses, microprobe analyses of main ores, and 40K-40Ar radiometric dating of igneous rocks. The publication includes detailed geologic, structural, stratigraphic, and geochronologic data. This work was part of a series of reports on the geology, geochemistry, and mineral resources of the Iditarod quadrangle, Alaska. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: http://doi.org/10.14509/2252.