Linear features in the Powder River basin, Wyoming and Montana, were interpreted from Landsat images and analyzed to define major lineaments. Lineaments identified include several that trend northwest and a prominent set that trends northeast. These lineaments represent broad (5-10 km or 3-6 mi) linear zones where smaller, parallel and subparallel linear features are concentrated at the surface. The smaller linear features are interpreted as possible expressions of joints, fractures, folds, or lithologic boundaries produced by periodic readjustment along basement-block boundaries.

The lineaments discussed in this report were visually interpreted from maps of linear features and contour maps showing concentrations of linear features. Lineaments were subsequently compared to mapped structures, outcrop patterns, geophysical data, and isopach maps to assess their geologic significance. Correlations of these lineaments with mapped structures, geophysical gradients, or facies changes strongly support the interpretation that they represent the surface expression of boundaries of crustal blocks that have been periodically reactivated through time. The northeast and northwest patterns provide evidence that a systematic, rectilinear pattern of crustal blocks formed early in the earth's history and has largely controlled subsequent adjustments of the earth's crust.

These findings suggest the potential for depositional control of sedimentary units by structural adjustments between basement blocks and, thus, lead to the conclusion that lineaments may be used as guides in petroleum and mineral exploration if favorable source and host rocks are present.