Lineaments mapped on satellite images in western South Dakota define a geometry of basement blocks, and paleotectonic activity on these lineament-bound blocks is recorded in sedimentary rocks. Mapping on seven Landsat images in an area of about 100,000 km2 reveals that lineaments are best developed along azimuths of N. 60° E. to N. 90° E. and N. 30° W. to N. 60° W. Although their exact structural nature and origin are not known, these features are visualized as major zones of weakness that subdivide the crystalline Precambrian basement into discrete blocks. Several of the most prominent surface lineaments can be related to basement faults. The blocks bounded by these lineaments constitute low-relief uplifts that define the southern margin of the Williston Basin.
During deposition of the Upper Cretaceous Pierre Shale, lineaments were the sites of tectonic activity. Members of the Pierre are relatively continuous throughout the area and are well dated by biostratigraphic zonation. The base of the Mobridge Member is the highest structural datum available for regional mapping. Northeast-trending surface lineaments near the White and Cheyenne Rivers have a clear expression on a subsurface structural map of this horizon. The Ardmore Bentonite Bed lies approximately 300 m (980 ft) below the Mobridge; subsurface structure contours on this datum show the active lineaments trending northwest. Isopach maps of two rock-stratigraphic units between the Ardmore and Mobridge reflect the shift in tectonic activity from early northwest sets of lineaments to later northeast trends.
