I think all above comments are correct... and I'd like to add something.
I have done serial soil analyses on my mountain patch, and found some interesting collaberative results to the above statements.
I have found that soil in the middle of the slope of the hillsides is poorer in nutrients than the top and the bottom of the same slope. I've proved it without doubt by the serial analysis I've had done on my areas. For example, in my areas, I've found that key values such as pH -as well as Ca- and several other micronutrients have values that are numerically less ----in the middle of the slope.
I'm sending soil from Patch Two out today, and I expect the same results... with some mild varriances or course.
I'm guessing that bigtime gullywasher rains wash nutrients from the top, pick up the middle area nutrients on the way down; and come to rest on the bottom of the slopes. Now if you combine that with the observations of shade, and moisture... hmmm....
Just my 2 cents worth....