I have thought about building a cabin or moving a trailer house to land in a forest where there is no for sale sign, or land on the side of the road. Is all unocuppied land still property of the U.S.? Is there a way to purchase land that does not have a For Sale sign on it? How does land purchase work? I live in the state of WA, but I was thinking of buying some land to put a modular/mobile home on, and laying it a foundation on the land.