Mark Twain National Forest (MTNF), est. 9/111939; 1.5 million acres (6,100 km²), 78,000 acres (320 km²) of which are Wilderness and National Scenic River area. MTNF spans 29 counties and represents 11% of all forested land in Missouri. Named for author Mark Twain, a Missouri native. Poplar Bluff Ranger District, Ripley County, MO.