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River Hills

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About the River Hills

The River Hills are a hilly upland region surrounding the floodplains of the Mississippi, Illinois, and Missouri, and lower Sangamon rivers, in the states of Illinois and Missouri; the region consists of seven discontinuous pieces, the largest of which is the region extending along the Missouri river.

This region consists of a heavily-dissected landscape of hills, bluffs, cliffs, and ravines. It is underlain by limestone and sandstone, and covered in thick loess deposits. This region was not glaciated in the most recent glacial period, but part of the region was glaciated in earlier periods. There are some areas of karst topography, with underwater streams, sinkholes, and caves cut out of the soluble limestone; these areas are more common in never-glaciated portions to the south of this region. Soils here tend to be deep both on flat uplands and bottomlands, but thin on the steep slopes, where there are frequent bedrock outcroppings. The soil in river valleys is fine-textured and ranges from moderately well-drained to poorly-drained.

This region was originally mostly forested, with forest types largely governed by moisture levels. Mesic sites supported sugar maple (Acer saccharum), American basswood (Tilia americana), and northern red oak (Quercus rubra). Drier sites supported black oak (Quercus velutina) and white oak (Quercus alba), and the driest ridgetops supported post oak (Quercus stellata). The moister bottomlands and floodplains supported silver maple (Acer saccharinum), eastern cottonwood (Populus deltoides), hickories (Carya sp.), and American sycamore (Platanus occidentalis).

This area has a mosaic of land use, but there is still extensive forest cover, with a forest composition largely similar to its original state. In the east and north of this region, it represents a critically important corridor of woodlands in broader surroundings where most of the forests have been cleared for agriculture. However, in the west, this region is less forested than the Ozarks to the south. There is a small amount of agriculture here, including both cropland and pastureland, mostly on the flatter uplands. The cropland mostly produces feed grain and hay for livestock. There is also some urban and suburban residential development, including the cities of Quincy, IL, Colombia, MO, Jefferson City, MO, and part of the St. Louis metro area, but by and large this area has been less developed for both agriculture and urbanization than its surroundings due to the steepness of its terrain.

Because this region extends over a large area, it borders many different regions. It surrounds the lower, flatter regions of the Upper Mississippi Alluvial Plain in the north and the Middle Mississippi Alluvial Plain in the south. Inland from the river, in the north it is bordered by the Western Dissected Illinoian Till Plain. Farther south, inland it is bordered to the east by the Southern Illinoian Till Plain. Along the east side of the Mississippi river, for a stretch it is replaced by the Karstic Northern Ozarkian River Bluffs. The southernmost section of it east of the Mississippi has four short borders to the east with the Northern Shawnee Hills, the Southern Shawnee Hills, the Wabash-Ohio Bottomlands, and the Northern Holocene Meander Belts.

In Missouri, the northernmost part of this region is bordered to the north by the Loess Flats and Till Plains. Inland from the rivers, much of it surrounds the Claypan Prairie. At its west end there are borders with the Rolling Loess Prairies, the Missouri Alluvial Plain (along the Missouri river), the Wooded Osage Plains to the west, and the Prairie Ozark Border to the south. There is a long border to the south with the Osage/Gasconade Hills, a short border with the Central Plateau, and then a border to the south, and a long border to the west along the Mississippi river with the Eastern Ozark Border. The very southern end also borders the St. Francis Lowlands.