Iowa is bordered on two sides by rivers; the Mississippi separates it on the east from Wisconsin and Illinois, and the Missouri and the Big Sioux separate it on the west from Nebraska and South Dakota. The state is bounded on the north by Minnesota and on the south by Missouri. Iowa is an area of rich, rolling plains, interrupted by many rivers. The terrain is low and gently sloping, except for the hills in the unglaciated area of NE Iowa, the steeply sloping bluffs on the banks of the Mississippi, and the moundlike bluffs on the banks of the Missouri. The rivers of the eastern two thirds of Iowa flow to the Mississippi; those of the west flow to the Missouri. The original woodlands, which included black walnut and hickory, were destroyed by lumbering and land clearing in the 19th cent., and present wooded sections are covered only with second or third growths of timber. Only 0.1% of Iowa, the lowest total in the 50 states, is owned by the federal government.
Historically typical of Iowa was the prairie. Covered a little more than a century ago with grass higher than the wheels of the pioneers' prairie schooners, or covered wagons, the prairies gave way to fields of corn and other grains. Wildflowers still brighten the roadsides, but few areas of the original grassland remain, and several prairie preserves have been established. The former habitat of wild turkeys, prairie chickens, and quail, Iowa abounds with migratory geese and ducks and the imported ring-necked pheasant and European partridge, all of which are hunted in the autumn.
Iowa's climate is continental—northwest winds drive the mercury down below 0°F ( - 18°C) in winter, and in the summer hot air masses bring oppressive heat; there are violent thunderstorms, hail, and occasional droughts. Floods have periodically inflicted great losses of life and property, necessitating control measures. In the devastating midwestern flood of 1993 all 99 counties of Iowa were declared disaster areas. Overall, the average annual rainfall in Iowa is 31 in. (78.7 cm), and, since most of this falls in summer, soil is often washed away. Iowans have had to fight erosion with modern plowing and planting practices, control of water flow, and reforestation. Still, Iowa has some of the most fertile agricultural land (about 70% of the state's area is cropland) in the world.