The integration of radar, magnetic, and terrain conductivity data in an archaeological investigation of a Hudson Bay's company fur trade post

In 1799, the site of Rocky Mountain House, Alberta, stood at the southwestern comer of the northern fur empires of the North West Company and their competition, the Hudson's Bay Company. Between 1799 and 1875, four forts were constructed by these companies at Rocky Mountain House. The third of these forts, which stood from 1835 until 1861, has been only partially excavated. The goal of this investigation was to evaluate the utility of geophysics as an archaeological aid in studying historic sites in Western Canada. The specific objectives were to identify the position of the rooms and palisades of the 1835 fort, and to locate burial sites associated with this and other forts. A challenging obstacle in describing the 1835 fort using geophysics is the fact that in 1861, the Blackfoot peoples burned the fort to the ground. Information from three geophysical methods are discussed. Ground penetrating radar data provided the greatest detail in describing fort construction and burial locations. The GPR data, however, would have been of limited use if not viewed in conjunction with the information provided by magnetic gradient, and terrain conductivity plots of the particular sites. The integration of the various methods provided an overall plan of the original construction of the 1835 fort. While GPR most clearly identified approximately 50 graves at one large cemetery, terrain conductivity mapping was superior in locating probable coffins at a second, smaller burial site. Beyond being a good example of an archaeogeophysical data set, the significance of this paper is the clarity with which it is shown the need to integrate a number of geophysical techniques at investigations of historic sites in Western Canada.