Southeastern United States, 193,000 mi2 (499,900 km2) This
province comprises the Piedmont and the irregular Gulf Coastal
Plains, where 50 to 80 percent of the area slopes gently toward
the sea. Local relief is 100 to 600 ft (30 to 180 m) on the Gulf
Coastal Plains, and 300 to 1,000 ft (90 to 300 m) on the
Piedmont. The flat coastal plains have gentle slopes and local
relief of less than 100 ft (30 m). Most of the numerous streams
in the region are sluggish; marshes, lakes, and swamps are
numerous. The climate is roughly uniform throughout the region.
Mild winters and hot, humid summers are the rule; the average
annual temperature is 60 to 70F (15 to 21C). The growing season
is long (200 to 300 days), but frost occurs nearly every winter.
Precipitation, which averages from 40 to 60 in (1,020 to 1,530
mm) annually, is rather evenly distributed throughout the year,
but peaks slightly in midsummer or early spring, when it falls
mostly during thunderstorms. Precipitation exceeds evaporation,
but summer droughts o