Between 1850 and 1871 the United States government used a portion of the public domain (federally owned land) to assist and encourage the building of railroads. In all, during that twenty-one year period approximately 1.31 million acres of land were transferred to private ownership. This represented 9.5 percent of the public domain as it stood in 1850 (1.39 billion acres). The land was located in twenty-seven states, but the largest grants were made in California (11.5 million acres), Kansas (8.2 million acres), Minnesota (9.9 million acres), Montana (14.7 million acres), North Dakota (10.6 million acres), and Washington (9.5 million acres). Although the program began in 1850, most of the grants were made under the terms of the Pacific Railway Act of 1862. This law was in effect from 1862 to 1871 and its purpose was to encourage the construction of the transcontinental railroads.