Arkansas River

The Arkansas River (Pawnee: Kícka ) is a major tributary of the Mississippi River. The Arkansas generally flows to the east and southeast as it traverses the US states of Colorado, Kansas, Oklahoma, and Arkansas. The river's initial basin starts in the Western United States in Colorado, specifically the Arkansas River Valley, where the headwaters derive from the snowpack in the Collegiate Peaks. Then it flows east into the Midwest via Kansas, and finally into the South through Oklahoma and Arkansas.

At 1,469 miles (2,364 km), 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 170,000 sq mi (440,300 km²). In terms of volume, the river is much smaller than both the Missouri and Ohio Rivers, with a mean discharge of roughly 41,000 cubic feet per second (1,200 m3/s).

The Arkansas from its headwaters to the 100th meridian west formed part of the US-Mexico border from the Adams-Onís Treaty (in force 1821) until the Texas Annexation or Treaty of Guadelupe Hidalgo.