Mark Twain National Forest (MTNF) is a US National Forest. It is mainly in the southern half of Missouri. The MTNF was established on September 11, 1939. It is named for author Mark Twain, a Missouri native. The MTNF covers , of which are wilderness, and National Wild and Scenic River area. MTNF spans 29 counties. It 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 cover nine overall unique tracts of forests. The headquarters of the MTNF are in Rolla, Missouri.