The Missouri and Arkansas River watersheds, spreading across more than 1 million square miles and 170,000 square miles, respectively, cover most of the American Great Plains. The divide between these watersheds begins on the Continental Divide, just west of Hoosier Pass in central Colorado; from there it runs southward along the crest of the Mosquito Range which separates the upper Arkansas Valley, to its west, from the broad expanse of South Park, to its east, which is drained by the South Platte River (a tributary of the Missouri).
After crossing Trout Creek Pass, the Missouri-Arkansas Divide curves eastward along the southern rim of South Park, running atop the volcanic Thirty-nine Mile Range before snaking northeastward through the Front Range foothills. Emerging onto the Colorado Piedmont, the divide follows the crest of the Palmer Divide, an erosional remnant of the High Plains that extends eastward from the foothills just north of Colorado Springs. After crossing I-70 north of Limon, the divide curves to the southeast, crossing the highway once again at Genoa, Colorado; from there it swings southward and then eastward along the southern edge of the Republican River watershed, a tributary of the Missouri.
Entering Kansas, the Missouri-Arkansas Divide follows the southern edge of the Smoky Hill and Kansas River watersheds before reaching southwest Missouri. There, this hydrologic barrier runs along the northern edge of the Neosho and White River watersheds (tributaries of the Arkansas), ending in the eastern Ozarks where short streams of southeastern Missouri and northeastern Arkansas empty directly into the Mississippi.
