In the 1850s, the border between the two colonies was established, with the idea that the border would follow the highest points of land. However, due to the difficult terrain and the lack of accurate surveying equipment at the time, the border was not always drawn in a straight line.
In some places, the border deviates from the watershed to include or exclude certain features, such as rivers or mountains. For example, the border around Stanthorpe was drawn to include the town within Queensland, while the border near Tenterfield was drawn to exclude the town from Queensland.
Additionally, the border was amended several times over the years to resolve disputes between the two colonies, resulting in the current irregular shape of the border.
