Date of this Version
In 1988 the U.S. Geological Survey published a radar image mosaic of an area roughly that of the Alliance. Nebraska 1° × 2° topographic map at the same scale, 1:250,000. Striking near-parallel valley trends in the vicinity of Chadron, Nebraska, may be related to jointing or possible faulting. Two sets, oriented approximately N30E and N28W, are obvious in the area east of Chadron. Sets south of Chadron on the Pine Ridge trend approximately N40E and N50W. On the Pine Ridge west of Fort Robinson in Sioux County some E-W and N-S features are also apparent. Other features that may be structurally related are prominent N20W and N30W drainages that cross Box Butte County and seem to continue into the Sand Hills affecting dune position. The Toadstool Park (?Whalen) Fault shown by DeGraw (1971, Figure 5) also appears present on the image.