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Show sylvania) ; and it contains three contrasting types of land. Within the basin are parts of the Coastal Plain, the Piedmont Plateau, and the Appalachian Mountains. The Coastal Plain section is broad and level, lying at low elevations adjacent to Chesapeake Bay. It is underlain to considerable depths by unconsoli- dated sands, gravels, and clays. The Piedmont Plateau, at the inner edge of the Coastal Plain, is underlain by hard, resistant rocks. Streams flowing across the Piedmont are charac- terized by falls and rapids at the point where they drop from the hard rocks of the Piedmont onto the soft materials of the Coastal Plain. Hence the boundary between the Piedmont and Coastal Plain is called the Fall Line. It is here that the Great Falls of the Potomac are found. The Piedmont is an area of moderately steep slopes and is generally well-dissected hilly terrain, in which the hills become higher toward the western margin. This is an area of serious soil erosion, con- tributing much to the silt load of the river. The headwaters of the Potomac River system rise in the Appalachian Mountain section. Moun- tain ridges occupy the eastern and western margin of this region but the center is the broad, limestone- floored, rich agricultural Shenandoah Valley. For the most part, agriculture is confined to the valley floors and lower ridge slopes. The high, long ridges are largely in forest. The climate of the basin is generally one of warm, humid summers and moderate winters. However, sub-zero temperatures occur annually in the moun- tains and occasionally over the entire area. Rain- fall averages about 38 inches (with 54 inches in the headwaters of the North Branch of the Potomac in West Virginia and 30 inches in the upper valley of the South Branch) and is fairly uniformly distrib- uted throughout the year. Rainfall generally fa- vors agriculture, although droughts have occurred. During the year, there are approximately 110 rainy days, and about 55 percent of the rainfall is between April and September. While not readily apparent from average monthly weather statistics, summer rainfall is frequently characterized by intense thunderstorms following occasional prolonged dry periods. These storms cause local flood conditions, retarded growth of crops, and crop damage from beating rains and hail. Average annual snowfall varies from 5 inches in coastal areas to 30 inches in the mountains, with occasional tieavy falls. The basin is also subject 578 to long-continued cyclonic storms, and to tropical hurricanes, which have produced disastrous floods. Rainfall in a 1942 storm reached nearly 19 inches in 93 hours. The People: Distribution and Population Growth About 2.3 million people live in the Potomac River Basin, over half of them in the metropolitan area of the Nation's capital.2 The preliminary count by the Bureau of the Census for 1950 places the Washington metropolitan area population at 1,452,000. The population gain in the last decade raises Washington from twelfth place in 1940 to eleventh place among metropolitan areas of the Nation. The largest hinterland urban areas are the cities of Cumberland and Hagerstown, Md. Hagers- town, according to the Census Bureau's preliminary count, increased its population from 32,491 in 1940 to 36,232 in 1950, whereas there has been a decrease in Cumberland population from 39,483 to 37,632 during the same period. Cumberland, whose econ- omy originally rested on coal mining but now de- pends primarily on a few large manufacturing industries, was designated in 1950 as a "distressed employment area." There has been little change in recent years in the number of rural people in the Potomac Basin. There has, however, been some recent increase in the number of small towns which were formerly classified as rural areas. Seventeen cities and towns now have populations over 5,000 and 122 have populations of 500 or more. The Economy The Potomac River Basin is unique in that the seat of the National Government is located within its limits. Government and activities directly asso- ciated with government are responsible for sustain- ing a large part of the basin's population. In 1950 the Federal civilian employment alone in the Wash- ington metropolitan area was 238,500. The em- ployment of this large staff of workers in "white 2 The metropolitan area includes the District of Colum- bia, Montgomery and Prince Georges Counties in Mary- land, and Alexandria, Arlington, and Fairfax Counties in Virginia. |