The Base Contour Revised
Crandell has suggested the 1220 meter contour as the base. However, even taking only the northwest quadrant alone, this contour cannot be used directly because it turns sharply before reaching the edge of the mask. The 1375 meter contour does approximate a circle and was used to make a mask.
Defining the Base
The mask was made by exporting the full image as a bitmap file, which was processed in a graphics program and reimported into IDRISI. The DEM was masked along the 1375 meter contour. The lower right corner is at 4290 meters, near the summit of Mount Shasta, 4316 meters. (The 1845 meter contour and Bolam Creek are for reference only.)The point protruding from the top of the quadrant was later removed from the model.
