The physical environment that constitutes the present United States can be characterized in terms of its area, location, climate, rainfall, and topography. Its total area is approximately 3.6 million square miles. The 48 contiguous states extend from the 24th parallel at the tip of Florida to the 49th parallel at their northern border with Canada, falling between 66 and 125 degrees west longitude. Alaska lies between 54 and 72 degrees north latitude and 130 degrees east longitude, with the westernmost point of the Aleutian Islands being in the Eastern Hemisphere at 172 degrees east longitude. The tropical Hawaiian Islands are situated between 19 and 25 north latitude and 155 and 176 west longitude.
The climate of the 48 mainland states is temperate, having cold winters and hot summers. The states east of the 100th meridian are characterized as humid, with 20-60 inches on average of annual rainfall distributed throughout the year; those west of the 100th meridian have an average between 5 and 20 inches, distributed mainly in the winter months. Topographically, the country extends westward from the Atlantic coastal plain at sea level upward to the Piedmont Plateau, between 500 and 1,000 feet in elevation, and the Appalachian Mountains, which rise to higher than 6,000 feet. Beyond the Mississippi River the elevation again rises gradually upward to about 4,000 feet, where the high plains approach the Rocky Mountains. The Rockies, Sierra Nevadas, and Cascades rise westward of the plains from around 4,000 to higher than 10,000 feet, interrupted by the intermontane Great Basin, between 4,000 and 6,000 feet above sea level. Westward of the Sierras, Cascades, and Coast Ranges, peaks in Alaska rise to 20,000 feet and in Hawaii to over 13,000 feet.
The country contains the rich natural resources required for agricultural and commercial systems. It has extensive forests in its eastern and western regions for fuel and building materials and extremely fertile soils along the eastern coastal plains, the Mississippi Valley, midwestern prairies, and Pacific coast valleys. Ample rainfall and water for agriculture are supplied from the snowmelts of the Appalachian Mountains to water the fertile soils of the eastern states. Snowmelt from the Rocky Mountains and Cascades fill the western river systems, while aquifers now supply water to the Great Plains, creating possibilities for irrigated agriculture in the arid regions of the West. The river systems and lowlands of the eastern coastal plains and Mississippi Valley make extended inland transportation and commerce feasible. The vast mineral treasury of the Appalachians and the western mountains, with their deposits of gold, silver, copper, iron, and coal, supply the energy and minerals needed for thriving industries. These natural features, resources, and climate patterns were utilized first by Native Americans and then by colonists from other continents to create subsistence- and market-oriented societies.
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