General Land Office Survey Plats of Oregon were made from the 1850s through the early-20th century. They are some of the most detailed maps existing about land-use and ownership during white settlement of Oregon. Each plat map covers 36 square miles and is designated by a Township/Range number from the U.S. Public Land Survey System.
Print copies of select General Land Office Cadastral Survey Plats for Oregon are in the Knight Library Map Collection. They are located in the USGS Topo Maps after the Washington 7.5' topographic maps and are sorted by township and range.
You may sometimes hear plat maps referred to as "Donation Land Claim Maps." The Oregon Donation Land Act of 1850 allowed white men (and mixed-heritage Native American/white men) who had arrived in Oregon before 1850 to work on a piece of land for four years and legally claim the land for themselves. Township/Range plat maps showing the location of these claims and claims under subsequent land distribution acts (for example the various Homestead Acts) were filed with the Office of the Survey General of Oregon and became part of the records of the General Land Survey and included in the mentioned databases.
The Land Ordinance of 1785 set up a standardized system where settlers could purchase title to farmland in the undeveloped US west. It also set up the US Public Land Survey System, that eventually covered over 3/4 of the area of the continental United States. This system is sometimes referred to as the Rectangular Survey System.