The close-up view at the right indicates the orientation of the mysterious grain. The location of the close-up is shown by the white box on the image above. Do you see other features aligned with the grain? What could have caused such a pervasive regional feature? |
Index map
A north-northwest-trending terrain texture,
or grain, evident as myriad aligned ridges and valleys carved
by segments of very small streams, pervades the northern and central
Great Plains. This
widely distributed pattern disappears north and east of the Pleistocene
glacial margin. Both regional tectonism (fine-scale fracturing
in the Earth's crust induced by opposing horizontal forces) and
surface processes (late-glacial wind action) have been suggested
for the origin of this widespread texture.
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