The foothills half of this county cannot take a tow-behind grinder
Slope is the access variable here, and the soil survey quantifies it. USDA-NRCS gives the Pacolet series, the eroded Piedmont soil, slopes "commonly 15 to 25 percent but range from 2 to 60 percent," while Cecil, on ridge tops and interstream divides, runs 0 to 25 percent.
North of the city, toward Travelers Rest, Slater-Marietta and Tigerville, that gradient decides whether a machine reaches the stump at all or the job needs a winch, a tracked unit or a grinder walked down a bank. Wet red clay on a sidehill is a traction problem before it is a time problem, so describe the route when you ask for a figure, not just the diameter.