Use of The Internet's Geospatial Data Sources In Preparation For Field Work
Jet Tilton
December 4, 2000

This project is done as a partial fulfillment for ES 551
Taught by Dr. James Aber at Emporia State University, Emporia, Kansas


The internet is now a valuable source for geospatial resources. Many different products are available, some only a download away, and others can be ordered from various vendors such as the United States Geological Survey (USGS) and other government agencies. Websites such as EarthExplorer (formerly GLIS) offer aerial photography, satellite images, and various maps from locations around the world, and some browse-quality images are adequate for familiarization about a potential research area, and can be downloaded via FTP for free. Other products, such as digital elevation models (DEMs) and digital raster graphics (DRGs), also can be downloaded for free from internet sources such as the GIS DataDepot, which offers DEMs and DRGs for every state in the U.S. The 7.5' DEMs are available in spatial data transfer standard (SDTS) format that corresponds to 1:24000 topographic quads.

Prospective Study Area

The hypothetical study area for this project is an area to the northwest of Van Horn, Texas, in Culberson County. This area has been visited by the author during the University of Texas at Dallas's Geology Field Camp during the Summer of 1993. The area of interest surrounds Tumbledown Mountain, which currently is mined for talc. This study area will be supplemented with aerial photos from the USGS's EarthExplorer, and DEMs and DRGs from the GIS DataDepot.

Geology of Van Horn Study Area

The rocks exposed in the Van Horn, Texas vicinity are interesting and important because they provide a complete transect across the Grenville tectonic front, from allochthonous rocks in the hinterland, to sedimentary successions deposited in the foreland (Soegaard and Callahan (1994), as quoted in Bickford et al. (2000)). The rocks at Van Horn were metamorphosed and deformed at upper to middle crustal levels, and are in many instances almost unmetamorphosed. The rocks exposed here in the Van Horn vicinity provide a clear link with the dominantly plutonic and volcanic rocks in the Franklin Mountains, north of El Paso, Texas (Bickford et al. 2000). Figure 1. shows a map of Precambrian rocks near Van Horn, and also shows the location of Tumbledown Mountain (northeastern part of diagram).

Figure 1. Geologic map of Precambrian rocks near Van Horn, Trans-Pecos region of West Texas (Bickford et al. 2000).

The Grenville Province is generally interpreted as recording a tectonic event where terranes were accreted to the southern and eastern margin of North America during a hard continental-continental collision in which deep crustal material was obducted between 1.3 and 1.0 Billion years ago. The contrast between the high-grade Grenvillian terranes of eastern North America and in the Llano Uplift, and the lower-grade less deformed rocks in far west Texas suggests a major change in tectonic style across the southern margin of Laurentia, and Bickford et al. (2000) believe that the Allamoore-Tumdledown sequence in the Van Horn area, and the correlative rocks in the Franklin Mountains were deposited in a rift basin(s), indicated by the sedimentary rock features and the bimodality of the volcanic suites (Bickford et al., 2000).

Click Here for examples of Geospatial Tools Downloaded Off the Internet


The Internet now provides a way for researchers or students to download free geospatial data such as DEMs, DRGs, and aerial photos, that could possibly aid in preparation of field work. Topographic maps, in digital raster graphic format, can now be downloaded and viewed digitally, and allow the researcher the opportunity to become familiar with an area's topography before having to order or locate paper maps.


Bickford, M.E, McLelland, J.M., Nielsen, K.C., and Soegaard, K., 2000. Geology and geochronology of Grenville-age rocks in the Van Horn and Franklin Mountains area, west Texas: Implications for the tectonic evolution of Laurentia during the Grenville. Geological Society of America Bulletin, v. 112, no. 7: 1134-1148.

GeoCommunity's GisDataDepot. URL:

Soegaard, K. and Callahan, D.M. 1994. Late Middle Proterozoic Hazel Formation near Van Horn, trans-Pecos Texas: Evidence for transpressive deformation in Grenvillian basement: Geological Society of America Bulletin, v. 106: 413-423.

USGS EarthExplorer (formerly GLIS). URL: