About the hardest thing to hunt in the North American West, probably behind Mountain Goat, is the high Altitude Mountain Sheep.  The sheep have a wide range moving from the foothills and mountain valleys to very high and rocky altitudes.  Then, there is the work in getting to the sheep and then finding and packing the animal out.  But a lot of the old time hunters during the fur-trade era prized the meat, the horns, and the hide.  I suppose the challenge played a part then just as it does now.  Anyway, the animals made you work hard for your success.