Linear features are relatively short, distinct, non-cultural linear elements mappable on Landsat multispectral scanner images (MSS). Most linear features are related to local topographic features, such as cliffs, slope breaks, narrow ridges, and stream valley segments that are interpreted as reflecting directed aspects of local geologic structure including faults, zones of fracturing (joints), and the strike of tilted beds. 6,050 linear features were mapped on computer-enhanced Landsat MSS images of 11 Landsat scenes covering an area from the Rio Grande rift zone on the east to the Grand Canyon on the west and from the San Juan Mountains, Colorado, on the north to the Mogollon Rim on the south. Computer-aided statistical analysis of the linear feature data revealed 5 statistically important trend intervals: 1.) N.10W.-N.16E., 2.) N.35-72E., 3.) N.33-59W., 4.) N.74-83W., and 5.) N.89-9-W. and N.89-90E. Subsequent analysis of the distribution of the linear features indicated that only the first three trend intervals are of regional geologic significance. Computer-generated maps of the linear features in each important trend interval were prepared, as well as contour maps showing the relative concentrations of linear features in each trend interval. These maps were then analyzed for patterns suggestive of possible regional tectonic lines. 20 possible tectonic lines, or lineaments, were interpreted from the maps. One lineament is defined by an obvious change in overall linear feature concentrations along a northwest-trending line cutting across northeastern Arizona. Linear features are abundant northeast of the line and relatively scarce to the southwest. The remaining 19 lineaments represent the axes of clusters of parallel linear features elongated in the direction of the linear feature trends. Most of these lineaments mark previously known structural zones controlled by linear features in the Precambrian basement or show newly recognized relationships to geological and/or geophysical patterns that suggest probable influence by buried basement features. The remaining few lineaments are not strongly correlative with geological or geophysical patterns, but on the basis of existing data they cannot be dismissed as being possible expressions of basement features. NO. OF DATA = 27044

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Aeromagnetic data from the Rolla 1° × 2° quadrangle, Missouri, displayed as a small‐scale, grey‐tone image, provide a lucid picture of basement features beneath sedimentary‐rock cover. Late‐stage “tin” granite plutons of the Proterozoic St. Francois magmatic terrane are clearly delineated. The plutons average about 11 km in diameter and occupy a significant fraction (12 percent) of the area surveyed. Gravity data require that certain plutons are at least 3 km thick. Most of the plutons are fat ovals in plan view and show no flattening trend or structural alignment. The ensemble indicates significant extension in an orthorhombic stress field, with the minimum compressional stress being vertical. Exposed St. Francois terrane volcanic rocks show a characteristic intricate pattern in the magnetic signature. This pattern is more widespread than the subsurface distribution of volcanic rocks indicated by drilling and likely also incorporates areas of St. Francois batholith granite. The horseshoe‐shaped trend of the southeast Missouri lead deposits may be crudely aligned with the edge of this intricately patterned unit. Small, very high‐amplitude magnetic anomalies occur over the well known magnetite‐bearing deposits of the region. The magnetic background for all these features is probably provided by extensive areas of the Butler‐Hill type biotite granite, characterized by large tracts of low magnetic intensity and a cobblestone‐like pattern of ring‐shaped, weak magnetic highs. Few of the many regional faults, calderas, ring complexes, and lineaments previously interpreted from geologic, geophysical, and remote sensing data are expressed in the aeromagnetic image.

As part of the Central Colorado Mineral Resource Assessment Project, the digital image data for four Landsat Thematic Mapper scenes covering central Colorado between Wyoming and New Mexico were acquired and band ratios were calculated after masking pixels dominated by vegetation, snow, and terrain shadows. Ratio values were visually enhanced by contrast stretching, revealing only those areas with strong responses (high ratio values). A color-ratio composite mosaic was prepared for the four scenes so that the distribution of potentially hydrothermally altered rocks could be visually evaluated. To provide a more useful input to a Geographic Information System-based mineral resource assessment, the information contained in the color-ratio composite raster image mosaic was converted to vectorbased polygons after thresholding to isolate the strongest ratio responses and spatial filtering to reduce vector complexity and isolate the largest occurrences of potentially hydrothermally altered rocks.