The Kansas River, also known as the Kaw, is a river in northeastern Kansas in the United States. It is the southwesternmost part of the Missouri River drainage, which is in turn the northwesternmost portion of the extensive Mississippi River drainage. Its two names both come from the Kanza (Kaw) people who once inhabited the area; Kansas was one of the anglicizations of the French transcription Cansez () of the original kką:ze. The city of Kansas City, Missouri, was named for the river, as was later the state of Kansas.
The river valley averages in width, with the widest points being between Wamego and Rossville, where it is up to wide, then narrowing to or less in places below Eudora and De Soto. Much of the river's watershed is dammed for flood control, but the Kansas River is generally free-flowing and has only minor obstructions, including diversion weirs and one low-impact hydroelectric dam.
Course
Beginning at the confluence of the Republican and Smoky Hill rivers, just east of aptly named Junction City (), the Kansas River flows some generally eastward to join the Missouri River at Kaw Point () in Kansas City. Dropping on its journey seaward, the water in the Kansas River falls less than . The Kansas River valley is only long; the surplus length of the river is due to meandering across the floodplain. The river's course roughly follows the maximum extent of a Pre-Illinoian glaciation, and the river likely began as a path of glacial meltwater drainage.
Drainage
The Kansas drains of land in Kansas (almost all of the northern half), along with in Nebraska and in Colorado, making a total of just over . When including the Republican River and its headwater tributaries, the Kansas River system has a length of , making it the 21st longest river system in the United States. Its highest headwaters are at about and extend nearly to Limon, Colorado. Much of the drainage of the river lies within the Great Plains, but the river itself exists entirely within the Mid Continent Region. The majority of the rest of the state is drained by the Arkansas (and its tributaries, the Neosho, Cimarron, and Verdigris, all three of which drain into the Arkansas in Oklahoma). A portion of central-eastern Kansas is drained by the Marais des Cygnes River, which flows into Missouri to meet the Missouri River. A small area in the extreme northeast part of the state drains directly into the Missouri. In the Kansas City metro area, some streams drain east into the Blue River tributary of the Missouri.
Geology
The Kansas River flows through what is known as the Stable Interior region. Since this region is near the center of the North American Plate, it has not experienced any extensive geologic faulting, folding, or mountain building in recent geologic time. From the confluence at Junction City, the river flows through limestone, shale, mudstone, and occasional sandstone strata that, except for diagenesis, remain largely undisturbed since deposition in shallow Carboniferous and Permian seas. The age of the rock exposed by the river becomes progressively older as the river moves downstream for two main reasons. First, downstream areas experience more erosion from increased flow, and second because the slight uplift of the Ozark dome to the southeast caused the strata in Kansas to dip very slightly to the west. The Smoky Hill River and Republican River tributaries reach far to the west into the Cretaceous deposits of the Western Interior Seaway and the Neogene Period deposits of material from the uplift of the Rocky Mountains, which created the Ogallala Formation.
All of the rocks in the eastern Kansas valley are sedimentary, ranging from Late Pennsylvanian (300 million years ago) through the Permian, with three notable exceptions from the Quaternary Period. The first is river sand and gravel deposits, which have been carried in largely from erosion of the Ogallala and Cretaceous rocks by the western extents of the Kansas River tributaries. Second, the retreat of the Kansan glaciation left behind a combination of ice- and meltwater-deposited sediments known as drifta, a poorly sorted mixture of clay, sand, gravel, and even large boulders that cover parts the Kansas River basin from the Big Blue River and eastward. The third is loess, a fine silt that may have originally been deposited by the melting water of the receding glaciers, then redeposited by the wind. The thickest loess deposits can be found in the northwest and north-central part of the Kansas River basin from southern Nebraska into northwest Kansas, as well as near the river's mouth.