The Texas Panhandle Plains were once home to the Southern Plains Bison Herd, which Charles Goodnight said ranged no farther north than the Arkansas River or south of the Wichita Mountains, and was thought to have been separated from the Northern Herd by the construction of the Transcontinental railroad in the 1840s. Prairie life depended on a repeating cycle in which lightning and periodic wildfires burned off woody vegetation, bison moved into the lush new growth to graze, and the disturbed, grazed ground then created habitat for smaller wildlife such as pronghorn antelope, lesser prairie chickens, and prairie dogs until brush returned and fire began the cycle again. Bison also shaped the prairie by scratching against objects, wallowing in dust and mud, spreading seeds and plant material in their coats, shedding winter hair in spring, and disturbing soil around wallows in ways that encouraged diverse plant growth and provided food for other animals. These vast prairies, formed about 10,000 years ago after the last Ice Age glaciers retreated, once covered millions of acres across the central United States, but most were later plowed under for agriculture and few were preserved as public lands. Native prairies supported a great diversity of wildlife, and in the early 1980s Texas Parks and Wildlife reseeded land beyond this site with native plants, beginning a long effort to recreate a mixed-grass prairie.