Entry_ID: (required) Entry_Title: Geologic map of the Dillon quadrangle, Summit and Grand Counties, Colorado Group: Data_Set_Citation Originator(s): Karl S. Kellogg Title: Geologic map of the Dillon quadrangle, Summit and Grand Counties, Colorado Publication: Miscellaneous Field Studies Map Publication_Date: 2002 Publication_Place: Denver, Colorado Publisher: U.S. Geological Survey Data_Presentation_Form: map URL: http://pubs.usgs.gov/mf/2002/mf-2390/ End_Group Keyword: geologic maps Keyword: geologic structure Keyword: bedrock geologic units Keyword: geospatial datasets Keyword: geology Keyword: Morrison Keyword: Dakota Keyword: Benton Keyword: Niobrara Keyword: Pierre Group: Temporal_Coverage Start_date: 2002 Stop_date: 2002 End_Group Data_Set_Progress: Complete Group: Spatial_Coverage Southernmost_Latitude: 39.625 Northernmost_Latitude: 39.750 Westernmost_Longitude: -106.125 Easternmost_Longitude: -106.0 End_Group Location: USA Location: Colorado Location: Summit County Location: Grand County Group: Data_Resolution Latitude_Resolution: 20 Longitude_Resolution: 20 End_Group Access_Constraints: none Use_Constraints: none. Acknowledgment of the U.S. Geological Survey would be appreciated in products derived from these data. Originating_Center: (required) Group: Data_Center Data_Center_Name: U.S. Geological Survey Central Publications Group Dataset_ID: USGS Miscellaneous Field Studies Map MF-2390 Group: Data_Center_Contact Last_name: U.S. Geological Survey Central Publications Group First_name: N/A Phone: 303-236-5486 Group: Address MS 902, Box 25046 DFC Lakewood, CO 80225-0046 End_Group End_Group End_Group Group: Distribution Distribution_Media: online Distribution_Format : ARCE Distribution_Size: 2.8 Fees: none End_Group Group: Distribution Distribution_Media: online Distribution_Format : Shapefile Distribution_Size: 2.8 Fees: none End_Group Group: Multimedia_Sample URL: http://pubs.usgs.gov/mf/2002/mf-2390/mf-2390.gif Format: GIF Caption: Reduced-size image of the map sheet, 288x305 pixels, 44k bytes. End_Group Group: Multimedia_Sample URL: http://pubs.usgs.gov/mf/2002/mf-2390/downloads/mf-2390.pdf Format: PDF Caption: Printable representation of map layout, 5.3 MB. End_Group Group: Reference End_Group Group: Summary To update and reinterpret earlier geologic mapping, and to achieve a uniform regional geologic database. New 1:24,000-scale geologic mapping along the Interstate-70 urban corridor in western Colorado, in support of the USGS Central Region State/USGS Cooperative Geologic Mapping Project, is contributing to a more complete understanding of the stratigraphy, structure, tectonic evolution, and hazard potential of this rapidly developing region. The 1:24,000-scale Dillon quadrangle is near the headwaters of the Blue River and straddles features of the Blue River graben (Kellogg, 1999), part of the northernmost reaches of the Rio Grande rift, a major late Oligocene to recent zone of extension that extends from Colorado to Mexico. The Williams Range thrust fault, the western structural margin of the Colorado Front Range, cuts through the center of the quadrangle, although is mostly covered by surficial deposits. The oldest rocks in the quadrangle underlie the Williams Fork Mountains and the ridge immediately east of South Fork Middle Fork River, and include biotite-sillimanite schist and gneiss, amphibolite, and migmatite that are intruded by granite inferred to be part of the 1,667-1,750 Ma Routt Plutonic Suite (Tweto, 1987). The oldest exposed sedimentary unit is the Upper Jurassic Morrison Formation, but Pennsylvanian Maroon Formation, a sequence of red sandstone, conglomerate, and interbedded shale, underlies the southern part of the quadrangle. The thickest sequence of sedimentary rocks is Cretaceous in age and includes at least 500 m of the Upper Cretaceous Pierre Shale. Surficial deposits include (1) an old, deeply dissected landslide deposit, possibly as old as Pliocene, on the west flank of the Williams Fork Mountains, (2) deeply weathered, very coarse gravel deposits underlying a mesa in the southwest part of the quadrangle (the Mesa Cortina subdivision. The gravels are gold bearing and were mined by hydraulic methods in the 1800s), (3) moderately to deeply weathered, widespread, bouldery material that is a combination of till of the Bull Lake glaciation, debris-flow deposits, landslide deposits, and possibly pre-Bull Lake till, (4) glacial deposits of both Bull Lake (middle Pleistocene) and Pinedale (late Pleistocene)glaciations, (5) recent landslide deposits, and (6)extensive colluvial and alluvial deposits. End_Group Group: DIF_Author Last_name: Schweitzer First_name: Peter Middle_name: N Email: pschweitzer@usgs.gov Phone: 703-648-6533 Group: Address Mail Stop 954 12201 Sunrise Valley Dr Reston, VA 20192-0002 USA End_Group End_Group DIF_Revision_Date: 20150204 Science_Review_Date: