Layer: Upper Pierre sand Base Extent (ID: 142)

Parent Layer: Upper Pierre sand Base Structure

Name: Upper Pierre sand Base Extent

Display Field: SHAPE_Length

Type: Feature Layer

Geometry Type: esriGeometryPolygon

Description: Tops data for selected contacts were exported from Petra©as SS values with X-Y coordinates in NAD 83 to be imported as X-Y data into ArcGIS. In ArcGIS© point data were hand-contoured as polylines in 50-foot intervals with contours extending well beyond the County edges or probable surface extents of the surfaces. Where surface geology allowed, contours were directed to intersect at known, or suspected, contact exposures.Contour line placement tolerance with data points is general because of uncertainty in well location and elevation data. Contour placement is within 25 feet (7.6 meter) of the data point, in general.Projection of the structural maps to the surface and generation of outcrop traces took several steps. Some iteration was used depending on matches of projections with known outcrop patterns. The following is the basic sequence.Convert stratigraphic surface polyline contours to raster images using ESRI© 3D Analyst - Raster InterpolationTopo to Raster Tool.Create surface topographic DEM corrected for Quaternary cover using ESRI© 3D Analyst - Raster Math MinusTool.Convert depth to stratigraphic surface raster to contours using ESRI© Spatial Analyst - Surface Contour Tool. Select contour interval of 50 or 100 feet.Select “0”value contour using standard ESRI© Selection - Select by AttributesTool. Export selected “0” contour to be used as outcrop trace.Create outcrop trace. At this point it was often necessary to subjectively select and smooth “0” value contours to create reasonable traces. The contour created in step 5 was often irregular, or had numerous outliers that needed to be eliminated. Occasionally the contour was manually modified using the ESRI© Editor - Adjust LineTool.Create extent polygon using the ESRI© Editor - CreateTool by adding a line encircling outside of the County boundary that intersected both ends of the “0” contour polyline. Then created a polygon file using ESRI© Data Management Features - Feature to Polygon Tool.This feature class was created in 2019 in ArcGIS for Desktop Version 6.2 (Build 9200); Esri ArcGIS 10.6.1.9270.

Copyright Text: This project was funded by a grant from the Colorado Water Conservation Board (CWCB) matched by the Colorado Geological Survey (CGS) through its Severance Tax Operational Funds. Many people contributed to this project indirectly over the years. Development of the generalized geologic map builds on many hours of field mapping by CGS and U.S. Geological Survey (USGS) geologists. In particular, the authors owe gratitude to Matt Morgan and Jon Thorson for their tireless detective efforts at the 1:24,000 quadrangle scale weaving the geologic history of the region. We would also like to recognize Matt Sares of the Colorado Division of Water Resources and his staff for their input with respect to the geology of the Denver basin.

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