The southern Part of Arkansas belongs to the Gulf Coastal Plains, the eastern side are the flood plains of the Mississippi river. Such lowlands have no caves or mines. But there are two areas of interest, the north-west corner of the state which belongs to the Ozarks is karstified and has many caves. As most of the Ozarks belongs to RegionMissouri, see this page for more information about the Ozarks. And the area west of Little Rock is hill country composed of crystalline rocks. The area is an important producer of minerals and gems, mostly quartz, but also other gems including diamonds. There are numerous mines, most of the fee mining type.