Geologic map of the Montoso Peak quadrangle, Santa Fe and Sandoval Counties, New Mexico By Ren A. Thompson, Mark R. Hudson, Ralph R. Shroba, Scott A. Minor, and David A. Sawyer 2011 Scientific Investigations Map 3179 ABSTRACT The Montoso Peak quadrangle is underlain by volcanic rocks and associated sediments of the Cerros del Rio volcanic field in the southern part of the Española Basin that record volcanic, faulting, alluvial, colluvial, and eolian processes over the past three million years. The geology was mapped from 1997 to 1999 and modified in 2004 to 2008. The geologic mapping was carried out in support of the U.S. Geological Survey (USGS) Rio Grande Basin Project, funded by the USGS National Cooperative Geologic mapping Program. The mapped distribution of units is based primarily on interpretation of 1:16,000-scale, color aerial photographs taken in 1992, and 1:40,000-scale, black-and-white, aerial photographs taken in 1996. Most of the contacts on the map were transferred from the aerial photographs using a photogrammetric stereoplotter and subsequently field checked for accuracy and revised based on field determination of allostratigraphic and lithostratigraphic units. Determination of lithostratigraphic units in volcanic deposits was aided by geochemical data, 40Ar/39Ar geochronology, aeromagnetic and paleomagnetic data. Supplemental revision of mapped contacts was based on interpretation of USGS 1-meter orthoimagery. This version of the Montoso Peak quadrangle geologic map uses a traditional USGS topographic base overlain on a shaded relief base generated from 10-m digital elevation model (DEM) data from the USGS National Elevation. Faults are identified with varying confidence levels in the map area.  Recognizing and mapping faults developed near the surface in young, brittle volcanic rocks is difficult because (1) they tend to form fractured zones tens of meters wide rather than discrete fault planes, (2) the youth of the deposits has allowed only modest displacements to accumulate for most faults, and (3) many may have significant strike-slip components that do not result in large vertical offsets that are readily apparent in offset of sub-horizontal contacts.  Those faults characterized as “certain” either have distinct offset of map units or had slip planes that were directly observed in the field.  Faults classed as “inferred” were traced based on linear alignments of geologic, topographic and aerial photo features such as vents, lava flow edges, and drainages inferred to preferentially develop on fractured rock.  Lineaments defined from magnetic anomalies form an additional constraint on potential fault locations.  DISCLAIMERS This database, identified as SIM3179, 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. DATA FILES The database can be downloaded via the Web from http://pubs.usgs.gov/sim/3179/. ArcInfo export files, ArcView shapefiles, and an ArcGIS geodatabase may be extracted from a zip-compressed file (SIMXXXX_GIS.zip). In addition, an Adobe Portable Document Format (PDF) file can be downloaded, from which paper copies may be printed. The data were compiled from field mapping. The primary mapping responsibilities were as follows. : Thompson and Hudson mapped the volcanic deposits and faults and prepared the digital compilation of the geologic map, Shroba mapped the surficial deposits, Hudson and Minor mapped surface exposures of faults, Hudson conducted paleomagnetic studies for stratigraphic correlations, and David A. Sawyer assisted with unit correlations with exposures on the adjoining Tetilla Peak quadrangle to the south (Sawyer and others, 2002 ). This geospatial database consists of ArcInfo export files (.e00), ArcView shapefiles, and ArcGIS geodatabase files contained in a zip archive See the list below. Please refer to the file SIM3130.met for detailed metadata documentation for this geospatial database. List of files: 00ReadMe.txt SIM3179_pamphlet.pdf SIM3179_map.pdf SIM3179.met Datafiles: MontosoBasemap.tif MontosoBasemap.tfw MontosoHillshade.tif MontosoHillshade.tfw Montoso.gdb directory (contains GIS data as geodatabase feature classes) Geology Contacts Dike Flow_Directions Lineament Polygons Samples Strike_Dip Unit_label Well_location SIM3179_shapefiles.zip directory: contacts.shp (dbf/prj/sbn/sbx/shp.xml/shx) Dike.shp (dbf/prj/sbn/sbx/shp.xml/shx) Flow_Directions.shp (dbf/prj/sbn/sbx/shp.xml/shx) Lineament.shp (dbf/prj/sbn/sbx/shp.xml/shx) Polygons.shp (dbf/prj/sbn/sbx/shp.xml/shx) Samples.shp (dbf/prj/sbn/sbx/shp.xml/shx) Strike_Dip.shp (dbf/prj/sbn/sbx/shp.xml/shx) Unit_Label.shp (dbf/prj/sbn/sbx/shp.xml/shx) Well_location.shp (dbf/prj/sbn/sbx/shp.xml/shx) HOW TO OBTAIN THE DIGITAL FILES The digital files constituting the geologic map database of this report can be obtained via the Internet from the U.S.Geological Survey publications website. Go to the web page at http://pubs.usgs.gov/sim/3179/ and follow the directions to download the files. 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.