In the mid-1950s, the Midwest, including Illinois, was covered by lush prairies blanketed with diverse varieties of grasses and wild flowers. Some grasses such as Big Bluestem, Prairie Cord and Indian grew so high that settlers on horseback could not see over them. These vast expanses provided a unique habitat for numerous species of insects, mammals and other animals. To survive the summer heat and inconsistent rainfall, prairie plants developed complex root systems that extend deep into the ground, acting like a sponge to retain water and helping prevent soil erosion. Plants also adapted to naturally occurring or intentionally started prairie fire, which removed dead growth, enabled some seeds to germinate and provided nutrients through ash residue. Illinois prairies before the coming of the Europeans included plants whose native root systems could grow up to fifteen or twenty feet deep, while turf grows only three inches deep.