DIGITAL DATABASE FOR THE QUATERNARY GEOLOGIC MAP OF THE SHELBY 1° X 2° QUADRANGLE, MONTANA OPEN-FILE REPORT 2012-1170 By David S. Fullerton, Roger B. Colton, and Charles A. Bush 2013 Open-File Report 2012-1170 INTRODUCTION Files available through this site represent the digital component of the SHELBY Quadrangle of the Quaternary Geologic Atlas of the U.S., Open-File Report 2012-1170. The files contain a ArcInfo geodatabase, and a PDF file of the report map. This map was prepared as a database for compilation of a Quaternary geologic map of the Lethbridge 4° × 6° quadrangle, United States and Canada. Letter symbols for the map units are those used for the same units in the Quaternary Geologic Atlas of the United States map series. The Shelby quadrangle encompasses approximately 16,084 km2 (6,210 mi2). The northern boundary is the Montana/ Saskatchewan (U.S./Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes the Sweet Grass Hills. The primary river is the Marias River. The ancestral Missouri River was diverted south of the Bearpaw Mountains by a Laurentide ice sheet. The fill in the buried ancestral valleys of the Missouri River and Marias River in the southeast quarter of the quadrangle contains a complex stratigraphy of fluvial, glaciofluvial, ice-contact, glacial, lacustrine, and eolian deposits. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (for example, ground-moraine deposits, end-moraine deposits, stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 21 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in pedology or agronomy. Rather, it is a generalized map of soils recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. On the glaciated plains, the surficial deposits are glacial, ice-contact, glaciofluvial, alluvial, lacustrine, eolian, colluvial, and mass-movement deposits. In the Sweet Grass Hills beyond the limit of Quaternary glaciation they are fluvial, colluvial, and mass-movement deposits. Till of late Wisconsin age is represented by three map units. Tills of Illinoian and pre-Illinoian glaciations are not mapped, but are widespread in the subsurface. Linear ice-molded landforms (primarily drumlins) indicate directions of ice flow during late Wisconsin glaciation. DISCLAIMERS This database, identified as OFR 2012-1170, has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty, expressed or implied is made regarding the display or utility of the data on any other system, or for general or scientific purposes, nor shall the act of distribution constitute such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. Although this information product, for the most part, is in the public domain, it also contains copyrighted material as noted in the text. Permission to reproduce copyrighted items for other than personal use must be secured from the copyright owner. CONTACT INFORMATION Charles A. Bush U.S. Geological Survey (303) 236-4723 cbush@usgs.gov CONTENTS README.txt OF12_1170_map.pdf Shelby.txt (metadata) The following ARC/INFO files are included in shelbyGIS.zip: GIS data: Shelby geology.gdb geo_net_polygon feature class includes polygons that are map units and open water Explanation of fields: GEOCODE--Refers to the type of polygon and is either the map unit symbol, Lake or River. MAPUNITS--A description of the deposits and materials that make up the map units; blank where not applicable. See map.pdf for full unit descriptions. AGE--Refers to the age of the map unit and is one of the following: HOLOCENE AND LATE WISCONSIN; HOLOCENE, LATE PLEISTOCENE AND MIDDLE PLEISTOCENE; HOLOCENE AND PLEISTOCENE; LATE WISCONSIN; PLEISTOCENE AND PLIOCENE; PRE-QUATERNARY; or blank where not applicable. See Shelbytext.doc for full unit descriptions. geo_net_arc feature class consists of the following field: LTYPE--Refers to the type of arc and is one of the following: Contact, Shoreline, or Map Boundary gla_lin_arc feature class contains representations of linear glacial features Explanation of fields: LTYPE describes the feature represented by the line and is one of the following: LIMIT OF LATE WISCONSIN GLACIATION ON THE SWEET GRASS HILLS; LIMIT OF ILLINOIAN GLACIATION ON THE SWEET GRASS HILLS; LIMIT OF A LATE WISCONSIN GLACIAL READVANCE, OR POSITION OF A SIGNIFICANT STILLSTAND OF AN ICE MARGIN; INFERRED LIMIT OF A GLACIAL READVANCE MARKED BY THE DISTAL MARGIN OF GLACIOTECTONIC DEPOSITS OR GLACIOTECTONIC STRUCTURES MARGINAL END MORAINE--Single till ridge deposited along the margin of an ice lobe INTERLOBATE MORAINE--Formed at the junction of two ice lobes; MINOR MORAINES--Annual moraines, small moraines, corrugated moraines, or transverse ridges. Composed chiefly of till. Most of the ridges delineate the configurations of vanished retreating ice margins. Local relief of ridges typically is 1-5 m ICE-MARGIN ALIGNMENT INTERPRETED FROM ICE-MARGIN DRAINAGE CHANNELS AND TILL RIDGES ICE-MOLDED OR ICE-SCOURED LANDFORM--Drumlin, rock drumlin, or fluting. Long axis of symbol is parallel to the direction of ice movement. Some symbols represent more than one landform ESKER--Subglacial or englacial stream deposit BURIED BEDROCK VALLEYS OF THE ANCESTRAL MARIAS AND MISSOURI RIVER gla_lin_arc Frequency - frequency table shelbyAV geo_net_arc.shp (.dbf/.prj/.sbn/.sbx/.shp.xml/.shx) geo_net_polygon.shp (.dbf/.prj/.sbn/.sbx/.shp.xml/.shx) gla_lin_arc.shp (.dbf/.prj/.sbn/.sbx/.shp.xml/.shx) INSTRUCTIONS AND DOCUMENTATION FOR U.S. GEOLOGICAL SURVEY OPEN-FILE REPORT 2012-1170 To access the data: The data files can be downloaded via the web from: http://pubs.usgs.gov/of/2012/1170/ The main product is a Portable Document Format (.pdf) map, which requires Adobe Acrobat for viewing. Acrobat software runs on a variety of systems, and is available for download free of charge from Adobe at http://www.adobe.com.