GEOLOGY, TOPOGRAPHY, and DEM's

Because geology controls topography, topography reflects geology. This relationship has long been recognized and used by field geologists (and photogeologists). There is now a new way to use topography: the USGS has digital topography (Digital Elevation Models or DEM's) for almost all of the U.S. EDCON-PRJ has applied its magnetic and gravity data processing routines to these data to enhance the geological, particularly structural, elements evidenced by the topography.

EDCON-PRJ is using the 30-meter by 30-meter grid data (7½-minute quadrangles), the highest definition data available. Digitizing errors and local step functions are often present in the data and can cause problems in subsequent filtering operations. EDCON-PRJ has developed software to significantly reduce such problems while preserving the necessary high-frequency character of the DEM, thus allowing the separation of the topographic features into various wavelengths that may be of geological or structural significance.

The analysis is intended to augment photogeologic interpretations by the isolation and easy recognition of selected topographic features. Used in conjunction with other data bases, such as mapped geology, magnetics, and gravity, the DEM analyses have been shown to be especially useful in the interpretation of structure, possibly buried plutons, altered or structurally disturbed areas, and possible pediment areas. When integrated with stream sediment geochemistry it may be useful in delineation of mineralized structures or geochemically anomalous areas.

To view a sample of the Iron Point quadrangle, Nevada in both black and white as well as color versions of the available products, click here.

EDCON-PRJ is offering the following basic products:

Color shaded-relief maps, scale 1:24,000:

1. Edited, "de-stepped" (smoothed) topography

2. High-pass filtered topography (de-emphasizes large-scale features, e.g. mountains, and enhances more subtle topographic features)

3. Horizontal gradient of the high-pass topography (emphasizes structural elements)

Digital grids of the above in ASCII xyz format

Additional products and customized displays are available. A price quotation can be obtained from Mr. Robert C. Johnson.

e-mail: robertj@prj.com