US-259 bypasses Idabel to the south and east, concurring with U.S. Highway 70 Bypass. East of Idabel, the bypass route ends, and US-259 begins a concurrency with mainline US-70 and SH-3. The three highways continue north to Broken Bow, where US-70 splits to the east toward DeQueen, Arkansas and SH-3 splits to the west, bound for Antlers. US-259 continues north alone, taking a winding path through the Ouachita Mountains of southeastern Oklahoma. The route passes Broken Bow Lake on its west side, with State Highway 259A serving as an access loop to the lake and Beavers Bend State Resort. Near the lake, US-259 crosses through the Ouachita National Forest for the first time. Near Smithville, the highway serves as the western terminus of State Highway 4.