repeated flooding of the adjacent Mississippi. Farther from the river, in the southeastern part of the state, the Grand Prairie has a more undulating landscape. Both are fertile agricultural areas. The Delta region is bisected by a geological formation known as Crowley's Ridge. A narrow band of rolling hills, Crowley's Ridge rises above the surrounding alluvial plain and underlies many of eastern Arkansas's major towns. Northwest Arkansas is part of the Ozark Plateau including the Ozark 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. These mountain ranges are part of the U.S. Interior Highlands region, the only major mountainous region between the Rocky Mountains and the Appalachian Mountains. The state's highest point is Mount Magazine in the Ouachita Mountains, which is above sea level. Arkansas is home to many caves, such as Blanchard Springs Caverns. The State Archeologist has catalogued more than 43,000 Native American living, hunting and tool-making sites, many of them Pre-Columbian burial mounds and rock shelters. Crater of Diamonds State Park near Murfreesboro is the world's only diamond-bearing site accessible to the public for digging. Arkansas is home to a dozen Wilderness Areas totaling . These areas are set aside for outdoor recreation and are open to hunting, fishing, hiking, and primitive camping. No mechanized vehicles nor developed campgrounds are allowed in these areas. Hydrology Arkansas has many rivers, lakes, and reservoirs within or along its borders. Major tributaries to the Mississippi River include the Arkansas River, the White River, and the St. Francis River. The Arkansas is fed by the Mulberry and Fourche LaFave Rivers in the Arkansas River Valley, which is also home to Lake Dardanelle. The Buffalo, Little Red, Black and Cache Rivers are all tributaries to the White River, which also empties into the Mississippi. Bayou Bartholomew and the Saline, Little Missouri, and Caddo Rivers are all tributaries to the Ouachita River in south Arkansas, which empties into the Mississippi in Louisiana. The Red River briefly forms the state's boundary with Texas. Arkansas has few natural lakes and many reservoirs, such as Bull Shoals Lake, Lake Ouachita, Greers Ferry Lake, Millwood Lake, Beaver Lake, Norfork Lake, DeGray Lake, and Lake Conway. Flora and fauna Arkansas's temperate deciduous forest is divided into three broad ecoregions: the Ozark, Ouachita-Appalachian Forests, the Mississippi Alluvial and Southeast