Final answer:
The Ouachita Mountains are found in Arkansas and extend into southeastern Oklahoma, forming part of a region that includes the Ozark Plateau.
Step-by-step explanation:
The Ouachita Mountains are a mountain range that extends from Arkansas into southeastern Oklahoma, near the Wichita Mountains, and are part of the physiographic region that includes the Ozark Plateau. This mountainous area is known for its distinct geological features and is evidence of ancient plate boundaries as indicated by aspects of the topography in the surrounding states such as Texas, Oklahoma, New Mexico, and Northeastern Mexico. The region in question is not part of the Mountain West, which covers a different array of states and mountain ranges including the Rocky Mountains, Sierra Nevada, Cascades, and various basins and plateaus in Western North America.