to the National Atlas Home page
About | Fact Sheets | Contact Us | Partners | Products | Site Map | FAQ | Help | Follow us on Twitter 
Part of Project LogoAgricultureBiologyBoundariesClimateEnvironmentGeologyGovernmentHistoryMappingPeopleTransportationWater
to the Interactive Map MakerMap LayersPrintable MapsWall MapsDynamic MapsArticlesMapping Professionals





 
Geology
Map Maker
Geologic Map
Shaded Relief
Map Layer
Generalized Geologic Map of the Conterminous United States
North America Shaded Relief
 

Article

  The North American Tapestry of Time and Terrain

Introduction
The Two Maps
Zoom In
Features
Legend and Rock Ages
Rock Types
Political Boundaries
Credits

  Features
 

Strange Grain

 
magnified area of unusual grain with arrow showing direction A north-northwest trending terrain texture, or grain, evident as myriad aligned ridges and valleys carved by 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 created by opposing horizontal forces) and surface processes (late-glacial wind) have been suggested for the origin of this widespread texture.
Close-up of
 upper great plains region, with box outlining area of opposite grain