Ok folks, and I do say thanks again for all the help. I have tried to put
all comments together, and take the good advice offered.
I think that I will go with a 30 inch deep hole, 18 inches square. This
is still overkill I know, but this is a heavy post, and near the top of a
mountain that get 80 mph winds at times.
So, about 18 inch sq hole, dug about 30 inches deep. Will put
the 6 X 6 beam in the center of the hole.
I come up with about 5 cubic feet of concrete.
40 lb bags create .3 of a cubic ft. So, it would seem that I
would need about (16) 40 lb bags.
A full cubic yard weighs nearly 4,000 lbs, so the 5 cubic feet should
weigh about 750 lbs. Yes, that should hold up my post and sign in any
Please alert me if I am way off base on my conclusions, and thanks again to
all for the nice input !!