Mark Twain National Forest (MTNF) is a U.S. National Forest located in the southern half of Missouri. MTNF was established on September 11, 1939. It is named for author Mark Twain, a Missouri native. The MTNF covers approximately 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. MTNF is divided into six distinct ranger districts: Ava-Cassville-Willow Springs, Eleven Point, Houston-Rolla-Cedar Creek, Poplar Bluff, Potosi-Fredericktown, and the Salem. The six ranger districts actually comprise nine overall unique tracts of forests. Its headquarters are in Rolla, Missouri.