High Quality Content by WIKIPEDIA articles! The Snake River Plain is a geologic feature located primarily within the state of Idaho in the United States of America. It stretches about 400 miles (640 km) westward from northwest of the state of Wyoming to the Idaho-Oregon border. The plain is a wide flat bow-shaped depression, and covers about a quarter of Idaho. Three major buttes dot the plain east of Arco, the largest being Big Southern Butte.