Yes, it's in Unapproachable East. But I mostly picked it because the geography mostly matches and it's fairly lightly covered in previous material which makes it a good candidate to plop something new in.That sounds about right. I'd cut it off with the southern border being before the Cloud Peaks. I'd suspect that it all depends on what edition/book you're reading.
This is an area that I'm not very familiar with, I dont even really remember what supplement its in? Is it in the 3E Unapproachable East? I remember the area being mentioned minimally here in there through 2E but I stopped reading a lot of sourcebooks to the degree I did before 3E so I only read a few or bits and pieces. Just had more important things to worry about at the time than RPGs so I dropped off for a few years.