In Reply #5, Maidenstone said
I suggest that a sheep walk is/was part of the mountain to which sheep on a named farm were hefted.
That sent me on a hunt which may have resulted in something of interest to the OP.
I could only find one farm of "686 acres with sheepwalk" in the census for the area in question in 1851. The farm was Nantllwyd, the head was a widow, Margaret Jones, occupation being farmers widow 686 acres including sheep walk.
In searching for that farm, I came across a blog that mentions a John Jones of Nantllwyd, in the right area ( I think!) who gave up some of the farm to have a church built on it, but he died before it was completed.
The problem I am having is that the writer jumps around in time and places, and I am not sure if they are still talking about the right area when they talk about John's role in the construction etc and there may be more than one farm with that name.
The blog is at
http://daibach-welldigger.blogspot.com/2011/07/soar-y-mynydd-revival-at-remotest.html If someone with better eyes than me wants to take a peek at it to confirm, just search the page for Nantllwyd.
Edit I just found a newspaper article from 1933 talking about this church, being the most remote chapel in Wales, which led me to this wiki article!
https://en.wikipedia.org/wiki/Soar_y_mynydd The History section matches that blog!