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Many people driving through central Illinois are bored by the monotony of the flat terrain and the never-ending sea of corn and soybeans. While this monotony may lull some drivers nearly to sleep, few people realize that the endless flatness was created by glaciers or that materials deposited or associated with this massive ice are nearly everywhere in Illinois. Perhaps even fewer realize the role of glaciers in preparing the way for tallgrass prairie, a landscape form that produced some of the richest agricultural soil in the world.

Although there is evidence of at least four glacial periods in Illinois, the last two, Wisconsinan and Illinoian, are the ones responsible for most of the surface features of the state today. The mountains of ice from the Illinoian glacial period of 125,000 years ago advanced within 10 miles of where Carbondale now stands. The exposed area of Illinoian glaciation in the southern third of the state, known as the Southern Till Plain, is characterized by a gently rolling topography, much unlike the nearly flat terrain of the area of Wisconsinan glaciation to the north.

The Wisconsinan glaciation, which ended about 13,000 years ago, was confined generally to the land lying north of Shelbyville and east of Peoria. The ice advanced and retreated numerous times during alternating cold and warm periods, creating a system of moraines or ridges along fronts of the massive ice. When the glacial ice melted, large lakes formed between these earthen dams near present-day Lake Michigan. The huge volume of water eventually broke through the moraines and began cascading down through what is now the Kankakee River area, carrying tremendous amounts of gravel, sand, and fine silt during an episode known today as the Kankakee Torrent.

When the floodwaters joined what is now the upper Illinois River, they remained confined to the narrow river valley that, at this location, is entrenched in bedrock. Upon reaching the wide valley below where the city of Hennepin stands, the floodwaters lost their velocity; and the massive volumes of gravel, sand, and silt were deposited. As the water receded, the silt dried and was blown throughout the state by strong westerly winds. Once deposited, this windblown silt became loess.

The climate continued to warm following the Kankakee Torrent, and oaks and hickories became the most common trees about 10,600 years ago. During a prolonged, hot, dry period about 8,300 years ago, prairie entered Illinois from the west and became established as the dominant vegetation type. The flat to gently rolling landscape created by the glaciers provided ideal terrain for the movement of fire, an agent that shaped and perpetuated the prairies for the next 8,000 years.

When pioneers entered Illinois in the early 1800s, they encountered vast seas of tall grass throughout the northern two-thirds of the state. Although the largest prairies were in the north, all but eight of the state’s 102 counties had prairies. Illinois was the first state encountered by settlers that had large grasslands, causing the application of the nickname "Prairie State."

The Grand Prairie

Wet sloughs and marshes abounded within the Grand Prairie. It was here that numerous waterfowl, cranes, songbirds, bison, muskrats, prairie chickens, and coyotes made their homes. The prairie or massasauga rattlesnake favored these wet sites; and nearby was the antidote for its bite, a plant known as the rattlesnake master. Together with the tall grasses, big bluestem, Indian grass, and wildflowers such as compass plant, Culver’s root, and prairie dock, this largest of the Illinois prairies stretched from horizon to horizon. The Grand Prairie, a flat to gently rolling area 80 miles wide and 100 miles long, contained over 5 million acres of prairie. Today, only a few acres of good-quality prairie remain among the graves of pioneers or in narrow bands along railroads. Goose Lake Prairie, the largest prairie preserve in the state, was intensively grazed for many years and is not considered as representative of the mesic, black soil prairie as are the smaller remnants at Weston, Paxton, and Loda cemeteries.

The Gray Prairies

The Gray or Southern Till Plain prairies existed within the area of Illinoian glaciation in the southern third of the state. These prairies resembled those in the Grand Prairie because they also consisted of big bluestem, Indian grass, and many wildflowers of the extensive prairies of northern Illinois. Although about 4 million acres of prairie once existed within the Southern Till Plain, under 5 acres of high-quality prairie remains today; and all of these remnants are along railroads, where their continued existence is precarious due to maintenance activities.

Sand Prairies

Sand prairies developed on the sand deposits along the Illinois, Mississippi, Green, and Kankakee rivers and the dunes of Lake Michigan. Some people refer to these sand prairies as a "little bit of the west in Illinois" due to the prevalence of plants and animals more commonly associated with the western states. The most important grasses of these areas are little bluestem, sand love grass, and sand reed grass; goat’s rue and prickly pear cactus, a western native, are two of the common wildflowers. Some unusual animals found in the sand prairies are badgers, pocket gophers, lark sparrows, six-lined racerunner lizards, Illinois chorus frogs, and Illinois mud turtles.

Remnants such as Sand Prairie–Scrub Oak Nature Preserve, Iroquois State Conservation Area, and Ayers Sand Prairie Nature Preserve all exist within these major sand areas. They are all sand prairies, but each prairie has its own set of distinct plants and animals. Visiting just one will not reveal the great diversity of the sand areas of Illinois.

Hill Prairies

High on the windswept bluffs of major rivers and their tributaries, hill or "goat" prairies occur on windblown silt or loess deposits. These sites are characterized by a west-facing aspect and rugged topography with considerable variation in local relief. The primary grasses of hill prairies are little bluestem and sideoats grama. Some of the common wildflowers are leadplant, purple prairie clover, and flowering spurge. The western slender glass lizard, a legless lizard that superficially resembles a snake, is common on some hill prairies. Several rare butterflies, such as the Ottoe skipper, and the prairie walking stick, an insect related to grasshoppers, are found in Illinois only in hill prairie communities.

Fults Hill Prairie along the Mississippi River in Monroe County and Revis Hill Prairie along the Sangamon River in Mason County are two of the largest hill prairie preserves in Illinois. Hill prairies along the Mississippi River support many distinctly western plants and animals, such as the plains prickly pear cactus and the plains scorpion.

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Prairies of the Driftless Area

Although most of Illinois was covered by ice during the glacial periods, certain parts of Illinois, including JoDaviess and Carroll counties, were never glaciated. This region is characterized by rolling hills and great variations in local relief. The soils of this area developed on loess that covered steep slopes or bedrock.

The prairies of this area, which developed on the rolling uplands, contain many plant species of the northern Great Plains, including the plains buttercup and the pasque flower. The most common grasses of these dry prairies are little bluestem and sideoats grama.

Disappearance of the Prairies

Although the prairies were a source of beauty and inspiration to many of the pioneers, others saw prairies as sources of diseases, biting flies, snakes, and fires—in fact, prairie fires were described as "the messenger of death" by some early writers. Efforts to convert this land to agriculture began in earnest in the early 1800s and were greatly accelerated by John Deere’s 1837 invention of the self-scouring steel plow, followed by the construction of railroads in the 1850s and 1860s. Sand prairies, due to their aridity, were among the last to be converted to agriculture. Hill prairies, seemingly safe on high, nearly inaccessible bluffs, were intensely grazed, while others have been lost to woody plant invasion.

Efforts began about 50 years ago to reconstruct some of the prairie that has been lost. Although much of the work of restor-ing prairies has taken place in the Chicago region and within the Grand Prairie, prairies have been restored in many parts of the state. Unfortunately, practically no work has been done in reconstructing hill prairies and sand prairies. These tasks must be addressed if Illinois is going to retain a diversity of prairies.

Where are the original prairies today in the Prairie State? They are not the neat and orderly rows of corn and soybeans, for these are sites that once were prairie. Prairies may be found by those who diligently seek them in pioneer cemeteries, along railroads, atop high bluffs, on dunes of sand along major rivers, or on the shores of Lake Michigan. 

Times sure have changed. Prairies were the talk of the town during pioneer times; now they are rarely mentioned outside of conservation circles. It is no wonder. With fewer than 2,000 acres remaining, many citizens of Illinois have never seen one. Conser-vationists believe that most people would be thrilled with prairies if they could only see one in full bloom on a beautiful summer morning. Let’s hope that the sun will always shine on these biological treasures in Illinois, the Prairie State.

William McClain is an adjunct research associate in botany at the Illinois State Museum in Springfield. He serves as a member of The Illinois Steward Advisory Board. Photos by Robert J. Reber.