Is there any snow,if there is snow and depending on time and daylight I would watch and see where he enters the timber and plan a stalk in the trees from above him on the ridge.

If there is no snow and it is late in the day I would take the shot assuming I'm shooting my 300 WSM.Cross wind of 10 mph left to right, would lead me to belive my bullet would drift about 15 inches,sighted dead on at 300 would give a bullet drop of around 16-17 inches.If he is walking left to right he would be moving at about 1mph,so I would aim for the top of the back and hold my vertical cross hair on line with the middle rib,take two deep breaths,hold squeeze.This should result in a mildle lung and heart shot about 4 inches up from the bottom of the chest.
That is the perfect senerio,granted if I had the time like I said I would try to close the distance 100 to 150 yds if possible and terrain,or plan a stalk.From down wind and above him,this should be fairly easy if he in not spookish.