INTEGRATED 1:100,000-SCALE SURFICIAL AND BEDROCK GEOLOGIC MAPPING OF THE INDIAN SPRINGS QUADRANGLE, NORTHWEST OF LAS VEGAS, NEVADA, USA

Following decades of work, principally funded by the National Cooperative Geologic Mapping Program (NCGMP) through the National Mapping Act, geologic maps at various scales are now available covering the entire United States. However, these maps are often not integrated, resulting in abrupt discontinuities that obstruct application of map data toward analyses that span map boundaries. We present a preliminary 1:100,000-scale digital geologic map for the Indian Springs 30’ × 60’ quadrangle, located slightly northwest of Las Vegas, Nevada, and part of a large transect in the Intermountain West where the U.S. Geological Survey is developing seamless geologic mapping at a target scale as fine as 1:100,000 to 1:250,000. Geologic mapping in this and nearby quadrangles is especially challenging because much of the area is within restricted military lands. In the early 1990s, P. L. Guth and J. C. Yount conducted original 1:100,000-scale geologic mapping and compiled work that was conducted before access was restricted in some areas. We digitized and updated their unpublished linework and unit designations for the Indian Springs quadrangle with the aid of modern high-resolution satellite photos and digital elevation models, supplemented by new fieldwork.

We also illustrate the novel workflow that we employed. Seamless digital compilation was conducted in separate databases for bedrock and surficial geology within a collaborative enterprise geodatabase that employed the Seamless Integrated Geologic Mapping (SIGMa) extension to the Geologic Map Schema (GeMS). Bedrock geology was projected below Quaternary cover, an approach that enables novel applications for end users including direct use of this map as an input for multiscale 3D modeling. To present the map product for this quadrangle, we subsequently integrated the surficial and bedrock maps, but they remain separate in the growing geodatabase. Our demonstration of these new approaches serves as an example of the workflow and database schemas that are being developed and employed by the U.S. Geological Survey as it builds a seamless geologic map at such fine scales for the United States.