That is a good question Glass. According to the Constitution for the United States of America the Congress is charged with disposing of the public lands and making all needful rules to do so. The Congress seems to have abided by the Constitution until gold was discovered in the westen states in 1848. Since 1850 The United States has held title to the public land in all of the new states that have been admitted to the Union. They did continue the homestead laws until sometime in the 20th century. In 1976 Congress changed the law saying the public lands will belong to the United States forever.

I am not sure when the BLM began creating hardships on ranchers and buying their property. The first I remember hearing about it was in the early 1970's. The mechanism they have used is to get the environmentalists to create a fuss on a particular area over some endangered species. The Federal government gives the environmentalists grant money, in turn the environmentalists sue the BLM using the federal funds to pay for the litigation. The courts favor the enviros. This in turn cause the BLM to cave to the demands of the environmental groups and turn against the ranchers. The rancher ends up bankrupt, the environmentalists buy up the property at pennies on the dollar and turn it over to the government.

Under the new (unconstitutional) law this newly acquired land is locked away forever in the possession of the federal government.