The Iowa-Cedar River drainage basin, which finds the larger of the two rivers, the Cedar, as a tributary to the smaller, is second in size of various inland river drainage basins in the state. The combined rivers drain 11,615 square miles or, roughly, one-fifth of the area of the state. The Iowa River, which has its source in Crystal Lake, in Hancock County, flows southeast for a distance of 329 miles and has a 685-foot fall from source to mouth. From its source the river has a gentle slope of 1.5 feet per mile till it reaches Franklin and Hardin Counties, where the gradient increases to 7.5 feet per mile. It levels off sharply below Iowa Falls and nearly returns to its original gradient. The valley of the Iowa is narrow and gives rise to only one important tributary, the English River, which enters the Iowa 30 miles above its junction with the Cedar
