Geologic Map of the San Marcos North Quadrangle and Adjacent Portions of the Mountain City and San Marcos South Quadrangles, Hays, Caldwell and Guadalupe Counties, Texas.

Abstract

“Process Steps: 1. Black and white paper copies of the 1:24,000 geologic maps in the 1976 Ph.D. thesis of T. W. Grimshaw were scanned, assembled into a single map and saved in Tagged Image File Format (tif) at 200 dpi and the original map size, then georeferenced in ArcGIS desktop ArcMap v. 10.1 to North American Datum 1983 geographic coordinates. Line work was digitized in heads-up mode, a map topology was created, and rock unit polygons were constructed and attributed with ArcGIS tools. 2. Digital base map data for the geologic map were assembled from the following US Geological Survey online sources: a) Roads, boundaries and structures from the National Map, 2013; b) Place names from the Geographic Names Information System, 2013; c) Hydrography from the National Hydrography Dataset, 2010; d) Elevation Data from the National Elevation Dataset, 2004. Base map contour lines and spot elevations were obtained from the Texas Natural Resources Information Service (TNRIS) in 2010. Vector base layers from these sources were edited where necessary to conform to locations displayed in one meter resolution digital orthophotos of the region in 2010 provided by TNRIS. 3. The completed vector geologic map and base layers were exported from ArcMap as collared and collarless jpeg images after projecting on-the-fly to the spatial references of interest (see below). World file coordinates were obtain by georeferenced these images and exporting them with referencing information in TIF format. KML (KMZ) and geoPDF versions of the map were created directly from the vector layers with options and tools in ArcGIS.