Bedrock geologic map of the Nashua South quadrangle, Hillsborough County, New Hampshire, and Middlesex County, Massachusetts

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Frequently anticipated questions:

What does this data set describe?

Title:
Bedrock geologic map of the Nashua South quadrangle, Hillsborough County, New Hampshire, and Middlesex County, Massachusetts
Abstract:
The bedrock geology of the 7.5-minute Nashua South, NH-MA quadrangle consists of deformed Silurian to Jurassic crystalline metamorphic and intrusive igneous rocks. The database includes contacts of bedrock geologic units, faults, outcrops, structural geologic information, and photos.
  1. How should this data set be cited?

    Walsh, Gregory J. , Jahns, Richard H. , and Aleinikoff, John N. , 2013, Bedrock geologic map of the Nashua South quadrangle, Hillsborough County, New Hampshire, and Middlesex County, Massachusetts: Scientific Investigations Map 3200, U.S. Geological Survey, Reston, Virginia.

    Online Links:

    Other_Citation_Details:
    Walsh, G.J., Jahns, R.H., and Aleinikoff, J.N., 2013, Bedrock geologic map of the Nashua South quadrangle, Hillsborough County, New Hampshire, and Middlesex County, Massachusetts: U.S. Geological Survey Scientific Investigations Map 3200, 1 sheet, scale 1:24,000, 31-p. pamphlet.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -71.499512
    East_Bounding_Coordinate: -71.374254
    North_Bounding_Coordinate: 42.750157
    South_Bounding_Coordinate: 42.625022

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 2006
    Ending_Date: 2013
    Currentness_Reference: publication date

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: Map

  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. It contains the following vector data types (SDTS terminology):

      • Complete chain (347)
      • Label point (137)
      • GT-polygon composed of chains (137)
      • Point (4)

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: State Plane Coordinate System 1983
      State_Plane_Coordinate_System:
      SPCS_Zone_Identifier: 2001
      Lambert_Conformal_Conic:
      Standard_Parallel: 41.716667
      Standard_Parallel: 42.683333
      Longitude_of_Central_Meridian: -71.500000
      Latitude_of_Projection_Origin: 41.000000
      False_Easting: 200000.000000
      False_Northing: 750000.000000

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.000100
      Ordinates (y-coordinates) are specified to the nearest 0.000100
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.

  7. How does the data set describe geographic features?

    Entity_and_Attribute_Overview:
    The geologic data layers in the GIS database of this report include (1) CONTAX (contacts) - Polygon and arc data layers of bedrock geologic map units, contacts, and faults, including a polygon attribute table, (2) EXPOSURE - Polygon and arc data layers of bedrock outcrops, (3) PHOTOS - Point locations and photographs of geology, and (4) STRUCTURE - Point data of structural observations.
    Entity_and_Attribute_Detail_Citation: <https://pubs.usgs.gov/sim/3200/Downloads/readme.txt>

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?

    Walsh and others (2013). Supersedes Jahns, R.H., Willard, M.E., and White, W.S., 1959, Preliminary bedrock geologic map of the Lowell-Westford area, Massachusetts: U.S. Geological Survey Open-File Report 59-70, scale 1:31,680, 1 map.

  3. To whom should users address questions about the data?

    U.S. Geological Survey
    Attn: Gregory J. Walsh
    Research Geologist
    P.O. Box 628
    Montpelier, Vermont 05601
    USA

    802-828-4528 (voice)
    802-828-4465 (FAX)
    gwalsh@usgs.gov

Why was the data set created?

The bedrock geology was mapped to study the tectonic history of the area and to provide a framework for ongoing hydrogeologic characterization of the fractured bedrock of Massachusetts and New Hampshire. The digital data are intended for use by all government, academic, commercial, or other agencies in need of digital geologic map information. The report contains a GIS database, large format color sheet and explanatory text pamphlet in Adobe Portable Document Format (PDF), and a readme.txt file.

How was the data set created?

  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    Date: 2013 (process 1 of 1)
    Geology mapped by Walsh in 2006, by Jahns in 1939-40 (MA) and 1951 (NH). Geochronology by Aleinikoff, 2007-08. A preliminary version of the geology of the Nashua South quadrangle was published by Jahns and others (1959). This report supersedes the Nashua South part of the 1959 report. Jahns, R.H., Willard, M.E., and White, W.S., 1959, Preliminary bedrock geologic map of the Lowell-Westford area, Massachusetts: U.S. Geological Survey Open-File Report 59-70, scale 1:31,680, 1 map. The geology was mapped during 2006 and 1939-1951. The bedrock geology was mapped using standard techniques. Location information during modern mapping was collected with a GPS receiver (GPS model: Garmin eTrex Venture). Locational data for historic data (1939-1951) was digitized by Walsh from scanned unpublished map sheets compiled by Richard Jahns. The 7.5-minute Nashua South quadrangle was formerly named the Tyngsborough quadrangle. Jahns mapped the New Hampshire part of the Tyngsborough quadrangle in 1951, and the Massachusetts part from 1939-40. Scanned copies of Jahns’ unpublished manuscript maps were obtained from the Richard Jahns Collection at the Branner Earth Sciences Library, Stanford University, Palo Alto, California. The line and polygon data were compiled in Adobe Illustrator over the topographic basemap. Field and compilation sheets were scanned and registered in Illustrator. Topographic basemap separates were scanned at 400 dpi. Line and polygon data were exported from Illustrator in DXF format to Arc/Info version 9.3. Point data by Walsh were collected with GPS and a hand-held 3COM Palm Pilot III PDA computer. Data from the PDA were imported to ArcGIS version 9.3 as ASCII text files and joined with GPS point data to create shapefiles. Jahn's strike and dip data were heads-up digitized in Arc/Info. The GPS data were collected in Latitude and Longitude in degrees minutes and seconds in WGS84 datum. GPS data were projected to the Massachusetts Stateplane coordinate system (FIPS Zone 2001) in NAD83 datum, with units in meters. GPS locations were compared to the topographic basemap of the area and repositioned to match the base. The original coordinates remain in the STRUCTURE database. After editing in Arc/Info, all arcs, polygons, and points were converted to shapefiles. Data in the Massachusetts State Plane coordinate system were re-projected to the New Hampshire State Plane coordinate system. Line and polygon data were edited in Arc/Info and converted to shapefiles. Shapefiles were plotted in ArcMap and exported to Illustrator. Final cartography was done in Adobe Illustrator.

    Person who carried out this activity:

    Gregory J. Walsh
    U.S. Geological Survey
    Geologist
    P.O. Box 628
    Montpelier, Vermont 05601
    USA

    802-828-4528 (voice)
    802-828-4465 (FAX)
    gwalsh@usgs.gov

    Hours_of_Service: 0900 to 1700 Eastern Standard Time
    Data sources produced in this process:
    • Walsh and others (2013)

  3. What similar or related data should the user be aware of?

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

  1. How well have the observations been checked?

    All attributes digitized during the creation process were verified by displaying the lines and points in the database with respect to the USGS 7.5-minute topographic base map (1:24,000 scale), but no formal tests were performed.

  2. How accurate are the geographic locations?

    The data were created on a USGS 7.5-minute topographic map at 1:24,000-scale. Therefore, the horizontal accuracy is assumed to be within National Map Accuracy Standards, with a horizontal accuracy of 45.6 feet at the 95% confidence level. Locational information in the field was provided by a Garmin eTrex Venture GPS receiver.

  3. How accurate are the heights or depths?

    The data were delineated on a USGS 7.5-minute topographic map at 1:24,000-scale. Therefore, the vertical accuracy is assumed to be within National Map Accuracy Standards, with a vertical accuracy of 11.9 feet at the 95% confidence level.

  4. Where are the gaps in the data? What is missing?

    The geologic contacts were delineated on a USGS 7.5-minute topographic map based on observations at the outcrops shown in the database. Not all outcrops within the area were identified or visited during mapping. The geologic contacts might change if additional outcrops are discovered or exposed as the natural land changes or as the result of development. The features in the database are not based on legal parcels or definitions.

  5. How consistent are the relationships among the observations, including topology?

    These data are believed to be logically consistent, though no tests were performed. Geometry is topologically clean.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints:
Although all data released in this report have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the functioning of the software. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Use_Constraints: none

  1. Who distributes the data set? (Distributor 1 of 1)

    U.S. Geological Survey
    Box 25286, Denver Federal Center
    Denver, Colorado 80225
    USA

    1-888-ASK-USGS (voice)
    ask@usgs.gov

    Hours_of_Service: 0900 to 1700 Mountain Standard Time
  2. What's the catalog number I need to order this data set?

    USGS Scientific Investigations Map 3200

  3. What legal disclaimers am I supposed to read?

    These data were prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, product or process disclosed in this report, and represents its use would not infringe privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data and related materials. Reference therein to any specific commercial product, process, or related service by trade name, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.

  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 04-Jan-2013
Metadata author:
USGS
Attn: Gregory J. Walsh
Research Geologist
P.O. Box 628
Montpelier, Vermont 05601
USA

802-828-4528 (voice)

Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

Generated by mp version 2.9.14 on Fri Jan 04 09:57:01 2013