This isn't exactly the same thing as your question, but may help your research.
Charlie & George Vandersluis have been climbing a lot of County highpoints, including those in Montana. According to Andy Martin's "County Highpoints" book, the highest point in Stillwater County, Montana is Mt. Wood at 12,649'. However, if you climb to the summit of Mt. Wood, look to your right & you'll see a higher point about 1/4 mile away and down the ridge. Charlie & George both believe this point is truely the highpoint of that County (as opposed to the actual summit of Mt. Wood), so you may want to study the topos to see if such a point is higher than the point you're looking at on Granite.