Which Arkansas river is one of the longest in the United States and flows through the state before joining the Mississippi?

The Arkansas River is one of the longest rivers in the United States, stretching approximately 1,460 miles from its headwaters in Colorado to its confluence with the Mississippi River in Arkansas. It flows through a significant portion of Arkansas, providing important resources for transportation, agriculture, and recreation within the state. Its vast watershed includes diverse ecosystems, making it a vital component of Arkansas's natural landscape and economy.

The Ouachita River, while significant, is shorter and does not stretch through as many regions as the Arkansas River. The White River, another vital waterway in Arkansas, is also important, but it does not have the same length or breadth of watershed that makes the Arkansas River stand out as one of the longest in the country. The Missouri River, although a long river, flows primarily through other states and does not flow through Arkansas. Thus, the Arkansas River is the correct choice, reflecting its notable length and flow through the state before it meets the Mississippi River.