The Corps of Engineers contract maintenance folks removed the cross-tie steps originally given in the clue. I've had to revise the clue and send you to the center of the road. The clue has been changed on the website also:

http://po8.com/letterbox/sweetwater/

Add 6 to the number of square feet in the ACA sail. Go to the campsite
post with that number. From the post walk 228 degrees for about 43 paces,
and you should be about in the center of the road between two yellow center stripes.
Stand in the center of the road and shoot a bearing of 274 degrees.
Walk about 58 paces to the second pine stump on that azimuth. From that
stump, go 120 degrees for 20 paces to another stump. The letterbox is at
that stump, and may be covered with some branches and pine needles.
Exchange stamp impressions, replace the box, and return to the road.

Jim