On April 22, 1889 at twelve o'clock noon, the Great Land Run of 1889 opened the Unassigned Lands in Indian Territory to settlement in what was possibly the most dramatic land settlement in United States history. Covering approximately 2,950 square miles in the central part of what would officially become the State of Oklahoma on November 16, 1907, these lands had been defined after the Civil War by policies and agreements imposed in 1866 on the Creek and Seminole Nations by the United States government. Although the federal government was to hold the land for other Indian tribes, that did not happen. In the late 1860s, David L. Payne led a movement to open the area for settlement, and his followers, known as Boomers, made several illegal attempts to settle there before being removed by the U.S. Cavalry. The United States Land Office began surveying the land into square-mile sections in 1870, and by 1887 the Santa Fe Railroad crossed Indian Territory and the Unassigned Lands. By January 1889, the Creek and Seminole Nations understood that the federal government intended to open the lands, and they agreed to release earlier agreements in exchange for modest compensation. The land was then opened under the Homestead Act, allowing any man or single woman over the age of 21 to claim 160 acres. In the days before the run, tens of thousands of prospective settlers gathered along the borders awaiting entry, while some early entrants called Sooners were caught and removed. More than 50,000 people are estimated to have taken part, arriving by train, horseback, wagon, and on foot, and by nightfall the future city of Norman had an estimated population of 150 citizens.