Early in the 19th century, surveyors operating under the authority of the U. S. Surveyor General began surveying lands that would eventually comprise the State of Illinois. The surveyors moved across the state laying out a rectangular grid system, known as the Public Land Survey System (PLS or PLSS).
The surveyors kept notes about the quality of the landscape and other “remarkable and permanent things.” Where possible, they also identified three to four “bearing trees” at each corner and mid-point on the grid so that the spot could be re-located in the future (in areas with no trees, they would construct mounds of soil as markers). For each tree, they recorded its common name, location, and size. The
surveyors also recorded similar information for any tree that fell directly on the line of their survey grid (called “line trees”). These plat maps and field notebooks contain a wealth of information about what the landscape was like before settlers came into the state - and the majority of trees described were oak species!