To the west of this central region lies the Missouri Slope, which constitutes the grazing-forage belt. Originally the farms here were much smaller than those in other parts of the State--with the repeal in 1891 of tree claim and preemption laws, homesteaders were limited to 160 acres of free land. For a few years the settlers on the Missouri Slope were able to file on desert claims, receiving one section at $1.25 an acre with the understanding that they would improve the land by irrigation; but so many people throughout the arid regions of the United States filed on such claims fraudulently that the act was finally amended to include the requirement that at least $3 an acre must be spent for irrigation. Despite this land limitation, many new settlers came to western North Dakota during the "back to the land" movement from 1900 to 1910. Besides the farmers who took up free land, there were many school teachers, laborers, and business and professional persons who followed that method, or took a commuted homestead by filing on land, staying there 14 months, and paying the Government $1.25 an acre. In this region, where it is estimated that 30 percent of the land is not suitable for cultivation, it was inevitable that many of these inexperienced persons should settle on worthless property. Experienced ranchers and farmers realized that only large farms could be operated profitably, and purchased homesteads from dissatisfied settlers. In this manner the size of farms increased, until now they run to 800 acres or more. The most fertile soil of the western region is in the valley of the Missouri. It was here that Verendrye, Lewis and Clark, Catlin, and other early explorers found the Mandan, Hidatsa, and Arikara women carefully cultivating their neat fields of corn, beans, squash, pumpkin, melons, and sunflowers. Lack of rainfall is the chief drawback to successful agriculture in the grazing-forage belt; but with irrigation, field crops can be raised dependably. The value of irrigation has been demonstrated by the success of the 20,319 acres immediately west of the Yellowstone River in western North Dakota, an area irrigated by the Bureau of Reclamation project of 1906. Similar projects are proposed in the basins of the Knife, Heart, and Grand Rivers. The grazing-forage belt as a whole, however, is not well suited to agriculture. Texas cattlemen, driving their herds through western Dakota to furnish beef for frontier military posts, saw its true value as a cattle country. The nutritive grasses and natural shelters make this an ideal cattle-raising section.