The Loess Hills located in Western Iowa near the Missouri River, were created 10,000- 20,000 years ago, near the end of the last ice age. When the Pleistocene glaciers began to melt, the Missouri Valley became a water channel. Each winter as the water froze again, sediments (silt, clay, fine sand) were left exposed. As high winds picked up soil, sand dunes were formed. The process repeated over thousands of years, making large dunes composed of loess, or loosely compacted yellowish-gray pieces of sediment. Over time, three layers developed: the Loveland layer, Post-Kansan layer and Post-Iowan layer. The Loveland Loess was formed during the melting of Kansan Glacier and is composed of a heavy, reddish clay. The Post-Kansan Loess is light blue and very fine, while the Post-Iowan Loess is the subsoil of the hills. The hills now reach 60 ft. in height and cover 640,000 acres of land. Topsoil soon developed on the dunes allowing grass prairies and forests to grow. Today, the hills are home to a variety of trees such as bur oak, red oak, black walnut, hickories, basswood, elms, ashes, Kentucky coffee tree, cottonwood, ironwood, and red cedar. In the time of the ice age, animals such as woolly mammoths, camels, giant beavers and sloths lived on the hills, with humans inhabiting the land for nearly 6,000 years. Today the Loess Hills are now home to animals such as the black bear, elk, buffalo, antelope and wolves. On the grassfields, prairie chickens, rattlesnakes, prairie mice, white-tail deer, raccoons, quail, pheasants, and wild turkey can be found. The hills are split into 5 unique units- Mondamin, Pisgah and Little Sioux are named for nearby town, Preparation Canyon Unit is named after a no longer existent settlement of Mormons, and the Gifford Unit is named after the late Dr. Gifford and is part of the administrative unit of the Loess Hills Forest.