The Interior River Valleys and Hills are located in the heart of the Mississippi River basin. This area is where massive rivers like the Ohio and Missouri meet the mighty Mississippi River. The region covers parts of southeast Iowa, southern and southwestern Illinois, eastern Missouri, southeastern Indiana, and western Kentucky. The landscape is made up of wide, flat-bottomed valleys, steep river bluffs, and rolling slopes. In Illinois and Indiana, you will find plains that were shaped by ancient glaciers. These valleys are often filled with rich layers of silt and wind-blown soil called loess, as well as deposits from ancient lakes. Much of the ground is made of sedimentary rock from the Carboniferous period, which was a time when huge forests once covered much of the Earth.

The weather in this region follows a humid continental pattern. This means summers are often hot and sticky, with temperatures regularly climbing into the 90s (32ºC). Winters can be quite harsh, with temperatures dropping well below freezing and sometimes reaching 0ºF (-18ºC) or even lower. Most areas receive about 41.6 in (1,057 mm) of rain and snow each year, with amounts ranging from 33.8 in (860 mm) to 52 in (1,320 mm). Because the region is in a central part of the country, it often experiences intense thunderstorms and even tornadoes during the spring and summer months. The growing season is relatively long, usually lasting between 170 and 220 days without a frost.

Water is a major part of this landscape. Many rivers and streams flow through the area all year long. In the lowlands, the riverbeds are mostly made of sand and silt, while the streams in the higher hills are much rockier. You can find many wetlands, oxbow lakes, and reservoirs tucked into the valleys. The soil here is very productive for plants. Most of the land features Alfisols and Mollisols, which are types of soil that stay moist and are great for growing things.

The plants and animals here depend heavily on the river systems. In the low-lying areas near the water, you might find thick swamp forests filled with silver maple, American elm, and green ash. Other trees like pecan, sycamore, honey locust, hickories, and black walnut also grow well in these moist spots. You can also find pin oak, bur oak, Shumard oak, cherrybark oak, overcup oak, swamp white oak, swamp chestnut oak, and sweetgum in these areas. In the higher and drier areas, forests are made of oak and hickory trees. This includes post oak, southern red oak, white oak, black oak, and shagbark hickory. Some spots have beech, yellow-poplar, sugar maple, and northern red oak instead. This variety of trees provides homes for many animals. White-tailed deer, badgers, weasels, and raccoons are common. You might also see bobwhite quail or the colorful Carolina chickadee. In the water, paddlefish and various types of small fish called darters live in the streams. You can also find interesting reptiles like the timber rattlesnake, copperbelly water snake, eastern box turtle, snapping turtle, and redback salamander.

People use much of this land for farming. About half of the region is used for crops like corn, soybeans, wheat, and hay, while another 30 percent is used for pastureland for animals. The rest is kept as forest. Some areas also produce oil, gas, and coal. A fun fact about this region is that the paddlefish, which lives in the rivers, is often called a river unicorn because of its unique look. Another interesting thing is that the rich, wind-blown loess soil in these valleys was actually carried by wind from other areas thousands of years ago!

Besa's Garden Escape

Planting Areas

Central bed

Honeysuckle replacement

Rain garden

Wildlife Features

About the Interior River Valleys and Hills ecoregion

About the Gravois Creek watershed