Arkansas is a land of mountains and valleys, thick forests and fertile plains. The so-called Lowlands are better known by names of their two regions, the Delta and the Grand Prairie. The Arkansas Delta is a flat landscape of rich alluvial soils formed by repeated flooding of the adjacent Mississippi. Further away from the river, in the southeast portion of the state, the Grand Prairie consists of a more undulating landscape. Both are fertile agricultural areas.

The Delta region is bisected by an unusual geological formation known as Crowley's Ridge. A narrow band of rolling hills, Crowley's Ridge rises from 250 to 500 feet (150 m) above the surrounding alluvial plain and underlies many of the major towns of eastern Arkansas.

Northwest Arkansas is part of the Ozark Plateau including the Boston Mountains, to the south are the Ouachita Mountains and these regions are divided by the Arkansas River; the southern and eastern parts of Arkansas are called the Lowlands. All of these mountains ranges are part of the U.S. Interior Highlands region, the only major mountainous region between the Rocky Mountains and the Appalachian Mountains. The highest point in the state is Mount Magazine in the Ozark Mountains; it rises to 2,753 feet (839 m) above sea level.

Arkansas is home to many caves, such as Blanchard Springs Caverns. It is currently the only U.S. state in which diamonds are mined.