The California miners spread the concept of mining claims to other mining districts all over the western United States. The US Congress legalized the practice in 1866, and amended it in the Mining Act of 1872. All land in the public domain, that is, federal land whose use has not been restricted by the government to some specific purpose, was subject to being claimed. The mining law has been changed numerous times, but still retains some features similar to those settled on by the California 49ers.