As glaciers receded towards the end of the Ice Age and turned ice into liquid, the Mississippi River grew longer and wider. Over time, the silt deposits of the Mississippi created some of the most fertile soil in the world, ideal for agriculture. The areas around the Mississippi are composed of thick regolith that is around thick. The Bootheel lies in the flood plain between the Mississippi and St. Francis rivers, so the land is very flat. Since clearing and drainage of wetlands in the early 20th century, it has been predominantly developed for agricultural purposes. Prior to the 20th century, it was mostly unsettled swampy forestland.