Multispectral scanner images obtained from satellites provide a unique regional perspective of geologic features on the earth's surface. Linear features observed on Landsat images are particularly conspicuous and can be mapped easily. In Montana, east of long. 110°W and in adjoining parts of Canada, the Dakotas, and Wyoming, linear features have been mapped on 14 images. Black and white film products in bands 5 and 7 at a scale of 1:1,000,000 were employed. Specific linear features observed on both bands were compiled on a mosaic covering more than 90,000 mi² (233,000 km²). Trends to the northwest and northeast are most common, but north-south and east-west linear features are also observed.

Four separate tectonic regions of the Montana plains seem to be characterized by different populations of linear features. In an area 100 mi (160 km) wide along the Canadian border, linear features trending northwest are common, and only a few local structures, such as Poplar and Bowdoin domes, are present. In the vicinity of the Central Montana uplift, east-west linear features are associated with features trending northwest and northeast. An area 80 mi (129 km) wide along the Wyoming border has linear features which trend dominantly north-south and east-west, although northeast and northwest trends are also present. This part of southern Montana includes the northern flanks of the Big Horn uplift, Powder River basin, and Black Hills uplift. In eastern Montana the western margin of t e Williston basin has linear features which trend mainly northeast and northwest; north-south and east-west trends are rare.

Published syntheses of geophysical, structural, and stratigraphic data can be used to establish the geologic significance of specific linear features. Magnetic, gravity, and seismic data suggest that linear features may reflect basement structural elements such as fault-bounded blocks. Some specific geologic structures shown on structure contour maps are marked by linear features. Examples include Bowdoin dome, portions of Cat Creek, Lake basin, and Nye-Bowler fault zones, Cedar Creek anticline, and the Brockton-Froid fault zone. Paleotectonic features interpreted from stratigraphic maps have surface expression on Landsat that have not been recognized previously. For example, the southern margin of the Alberta shelf (Mississippian) appears to correspond with a zone of concentrated eas -west linear features in north-central Montana.

End_of_Article - Last_Page 1355------------