<P> At Cañon City, Colorado, the Arkansas River valley widens and flattens markedly . Just west of Pueblo, Colorado, the river enters the Great Plains . Through the rest of Colorado, Kansas, and much of Oklahoma, it is a typical Great Plains riverway, with wide, shallow banks subject to seasonal flooding and periods of dwindling flow . Tributaries include the Cimarron River and the Salt Fork Arkansas River . </P> <P> In eastern Oklahoma the river begins to widen further into a more contained consistent channel . To maintain more reliable flow rates, a series of large reservoir lakes have been built on the Arkansas and its intersecting tributaries including the Canadian, Verdigris, Neosho (Grand), Illinois, and Poteau rivers . These locks and dams allow the river to be navigable by barges and large river craft downriver of Muskogee, Oklahoma, where the McClellan - Kerr Arkansas River Navigation System joins in with the Verdigris River . </P> <P> Into western Arkansas, the river path works between the encroaching Boston and Ouachita Mountains, including many isolated, flat - topped mesas, buttes, or monadnocks such as Mount Nebo, Petit Jean Mountain, and Mount Magazine, the highest point in the state . The river valley then expands as it encounters much flatter land beginning just west of Little Rock, Arkansas . It continues eastward across the plains and forests of eastern Arkansas until it flows into the Mississippi River . </P> <P> Water flow in the Arkansas River (as measured in central Kansas) has dropped from approximately 248 cubic feet per second (7 m3 / s) average from 1944 - 1963 to 53 cubic feet per second (1.5 m3 / s) average from 1984--2003, largely because of the pumping of groundwater for irrigation in eastern Colorado and western Kansas . </P>

Where does the arkansas river join the mississippi river