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Geomorphic Regions of the United States

Geomorphologists–scientists who study the landforms of Earth–have divided the United States into physical regions called geomorphic (or physiographic) provinces.  Generally, the landforms, geological structure and often rock types, as well as the geomorphic history are similar within each province and significantly different from those of adjacent provinces.  Several geomorphic classifications of the United States have been devised.  One of the most commonly used classifications is presented in a  map produced by the United States Geological Survey (USGS):  Physical Divisions of the United States.  This map divides the 48 conterminous (contiguous) states into eight major divisions and 25 provinces; many provinces are subdivided into sections.  Alaska and Hawaii are not included on this map.  A more recent classification, also by the USGS divides the entire United States, including Alaska and Hawaii (although they are not shown on the main map), into 12 provinces.  These provinces are somewhat similar to the major divisions (some of which were groupings of provinces) on the earlier map.

The classification used in this book is an adaptation of these two maps with very minor modifications.  The conterminous states are divided into 23 provinces.  A very small portion of northern New York and northwestern Vermont is an extension of a primarily Canadian province–the St. Lawrence Valley province, and is not discussed in this book.  A small part of the southwestern  corner of California is an extension of a primarily Mexican province–the Lower California province.  Neither of these two extensions is generally considered a main province of the United States.  The small portion of the Lower California province that is in the United States is briefly discussed at the end of the chapter dealing with the Pacific Border province.  Alaska is divided into four provinces.  The Hawaiian Islands, although exhibiting a variety of landforms, are most commonly treated as one province and are categorized as such here.  Thus the United States, excluding non-state areas, is divided into 28 geomorphic provinces.

Non-state areas of the United States, such as Puerto Rico, the United States Virgin Islands, and American Samoa are not included here.  The geomorphology of Puerto Rico is discussed in Natural Regions of the United States and Canada (Hunt, 1974).  Virgin Islands National Park, as well as Buck Island Reef National Monument–one of the two national monuments in the United States Virgin Islands (the other is Virgin Islands Coral Reef National Monument), are discussed in The Geologic Story of the National Parks and Monuments (Harris and Kiver, 1985).  Virgin Islands National Park is also discussed in Geology of National Parks (Harris, Tuttle and Tuttle, 1997); this book also contains a chapter on the National Park of American Samoa (also called American Samoa National Park) in the United States territory of American Samoa.

This book has several predecessors, all of which are now out of print.  The first book mostly concerned with the regional geomorphology of the United States was Forest Physiography (Bowman, 1911), which despite its title was largely devoted to discussing geomorphic characteristics of the country.  Later books included Physiography of Western United States (Fenneman, 1931),  Physiography of the United States (Loomis, 1937), and Physiography of Eastern United States (Fenneman, 1938).  Although Physiographic Provinces of North America (Atwood, 1940) dealt somewhat with regional geomorphology, its emphasis was on geography and only superficially treated geomorphic provinces.  Thornbury (1965) in his Regional Geomorphology of the United States included a detailed chapter on the background of regional geomorphology of the country and laid the foundation for future books on the topic.  Natural Regions of the United States and Canada (Hunt, 1974) was an “expansion and revision” of Physiography of the United States (1967; different than the similarly-titled book written by Loomis in 1937).  Pirkle and Yoho produced Natural Landscapes of the United States in 1975, which continued through a revised and updated fifth edition by Henry and Mossa (1995).

Related books, some of which are still in print, include The Evolution of North America (King, revised edition 1977), Geomorphic Systems of North America (Graf, ed., 1987) and The Physical Geography of North America (Orme, ed., 2002).  Also, as previously noted, several books have been written about the geomorphology/geology of national parks in the United States, including:  1) Geology of Selected National Parks and Monuments (Fleisher, 1975); 2) The Geologic Story of the National Parks and Monuments (Harris and Kiver, 1985); and 3) Geology of National Parks (Harris, Tuttle and Tuttle, 1997).

Although relying on its predecessors, with the authors owing gratitude especially to Pirkle and Yoho to whom this book is dedicated, the present text is a completely new, begin-from-scratch endeavor.  As such, any errors, inconsistencies and shortcomings in this book are solely the responsibility of the authors, particularly the lead author.

The terms geomorphology and physiography, as originally used, had slightly different meanings, although they were often used interchangeably.  The term physiography has undergone several changes in usage and definition, and according to the Dictionary of Geological Terms (Bates and Jackson, eds., 1984) the term physiography now is “...obsolescent and is replaced by geomorphology.”  The term geomorphology (and geomorphic) will be used in this book.

Text by Jim Henry (Copyright 2007).
Illustrations by Miller Wylie and Mark Abolins.

Feedback is welcome.  Please e-mail Mark Abolins.