Cross-section of the Eastern Mountains (not to scale)
From the Pepperfields, it appears there is another cliff face to the north, upon which is located the Looming Fortress and beyond is the North Pinewood Hold. The valley of the Laughing River is to the southwest, and Castle Redface (and Mount Bli'aard) is to the southeast.
From Castle Redface, the layout is as described here:
So, very roughly, the area appears to look something like this:
Rough Map of the Pepperfields (not to scale)
Unfortunately, the only measurements given between any of these places do not appear to be useful:
Fifty leagues is presumably 150 miles, unless the measurement is, as suggested, by the Easterner's reckoning (in which case the measurement is meaningless, as there is no description given of how many miles that might be), but this is almost certainly not the case, as 150 miles north of the Laughing River would put Sandyhome in the middle of the Spearhead Channel on Steve's Map.
About the only piece of information we can be relatively certain of is that, since both measurements are given as 50 leagues, and in the same general passage, the Pepperfields are presumably exactly midway between Redface and Sandyhome.
Since all these places border each other, but not much in the way of actionable distances are given, and they're located within a mountain range, I decided to map out this area with the assistance of a hex map.
I made each hex be 25 miles across, positioned so that the Laughing River mostly flowed along edges. You can think of each hex as being analogous to an individual mountain or peak within the range.
I then located these places as follows;
I put Whitecrown in the center of the hex south of Lake Fenarr, Mount Bli'aard in the center of the hex west (and a little south) of Lake Fenarr, and Mount Kieron in the hex west (and a little north) of Mount Bli'aard.
In the hex north of Mount Bli'aard, I put the Pepperfields about 1/3rd of the way up the hex north, the North Pinewood Hold 2/3rds of the way north, and the Valley of Salt along the border between that northern hex and the hex to the north of it.
That hex (the one just north of the Valley) represents the downward slope of the Eastern Mountains, and ends very near to the Spearhead Channel; I put Sandyhome in the center of that hex, and my guess is that it gets its name because it is near to the coast.
I put Castle Redface just north of the southern edge of the hex that I believe represents Mount Bli'aard.
The Pepperfields, visualized on a 25 mile hex grid
That results in the Pepperfields being almost exactly between Castle Redface and Sandyhome (about 30 miles from each of them).
I believe Castle Redface is located in the County of Korio based on this passage:
In the Duchy of Eastmanswatch:
Miska
Vlad is given a county near to the Pepperfields:
I located Miska midway between the Pepperfields and Mount Kieron.