Concept
The Arkansas River is a major tributary of the Mississippi River. It generally flows to the east and southeast as it traverses the U.S. states of Colorado, Kansas, Oklahoma, and Arkansas. The river's source basin lies in Colorado, specifically the Arkansas River Valley. The headwaters derive from the snowpack in the Sawatch and Mosquito mountain ranges. It flows east into Kansas and finally through Oklahoma and Arkansas, where it meets the Mississippi River. At , it is the sixth-longest river in the United States, the second-longest tributary in the Mississippi–Missouri system, and the 45th longest river in the world. Its origin is in the Rocky Mountains in Lake County, Colorado, near Leadville. In 1859, placer gold discovered in the Leadville area brought thousands seeking to strike it rich, but the easily recovered placer gold was quickly exhausted. The Arkansas River's mouth is at Napoleon, Arkansas, and its drainage basin covers nearly . Its volume is much smaller than the Missouri and Ohio rivers, with a mean discharge of about . The Arkansas from its headwaters to the 100th meridian west formed part of the U.S.–Mexico border from the Adams–Onís Treaty (in force 1821) until the Texas Annexation or Treaty of Guadalupe Hidalgo. Name pronunciation varies by state. Generally, the river is pronounced ɑrˈkænzəs in Kansas, but ˈɑrkənsɔː in Colorado, Oklahoma and Arkansas. The path of the Arkansas River has changed over time. Sediments from the river found in a palaeochannel next to Nolan, a site in the Tensas Basin, show that part of the river's meander belt flowed through up to 3200 BCE. While it was previously thought that this relict channel was active at the same time as another relict of Mississippi River's meander belt, it has been shown that this channel of the Arkansas was inactive approximately 400 years before the Mississippi channel was active. The Arkansas has three distinct sections in its long path through central North America.
