An interpretative tool that can help make sense out
of the large amount of information contained in this map is the
regional classification shown here. Geomorphic, or physiographic,
regions are broad-scale subdivisions based on terrain texture, rock
type, and geologic structure and history. Nevin Fenneman's (1946)
three-tiered classification of the United States - by division,
province, and section - has provided an enduring spatial
organization for the great variety of physical features. The composite
image presented here clearly shows the topographic textures and
generalized geology (by age) from which the physical regions were
synthesized. The features
we describe represent many of these subdivisions.
PHYSIOGRAPHIC REGIONS OF THE LOWER 48 UNITED STATES
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