KENTUCKY, lying on the western slope of the Alleghenies, is bounded on the north by the northern bank of the Ohio River, on the northeast and southeast by West Virginia and Virginia, on the south by Tennessee, and on the west by the Mississippi River. Its greatest length, east to west, is 425 miles; its greatest breadth 182 miles. The total area is 40,598 square miles, including 417 miles of water surface.
"A peculiar situation exists at the extreme southwest corner," the U. S. Geological Survey Bulletin 817 states, "where, owing to a double bend in the Mississippi River, there is an area of about 10 square miles belonging to Kentucky that cannot be reached from the rest of the State without passing through a part of Missouri or Tennessee."
The State's topographic variations are mainly the result of slow or rapid erosion, according to the degree of resistance encountered in particular rock strata. The mountains in the sandstone region, the occasional deep gorges or underground drainage systems in the limestone area, and the swamp flats and oxbow lagoons in the far western part of the State, indicate the force, extent, and direction of erosive processes. Reelfoot Lake, in the far southwest, resulted from the earthquake of 1811-12. It is the only lake of importance in Kentucky, although the edge of the Highland Rim Plateau in the southwest is pocked with numerous small bodies of still water. These are sinkholes which have choked with vegetable matter and retained the water that drained into them.
The Ohio and Mississippi Rivers flow west and south, and form the State's main drainage channel. The Cumberland River, except for a small portion in the south-central region, the Big Sandy, the Licking, the Kentucky, the Green, the Tradewater, and the Tennessee Rivers follow the general northwest slope of the Allegheny Plateau. About 3,000 miles of river course are navigable.
Kentucky has six natural physiographic regions: (1) Mountain, (2)