Spirit Level

The Mullan Road was designed to facilitate the movement of troops and supplies across the Rocky Mountains between the Missouri River basin in the Great Plains and the Columbia River Basin at the Columbia Plateau during times of Indian hostilities. But because peace was reached with the Northwest Indians early on, the road was used only once (in 1860) for military means. Instead, it became a popular thoroughfare for emigrants and fortune-seekers during the Montana and Idaho gold rushes of the 1860s. 

The granite milestones marking the Mason-Dixon Line bear crests from the two parties involved in the land-grant dispute, the families of William Penn and Charles Calvert (also known as Lord Baltimore).