North-east of TaeMoCo Mine you can find a passage between two large masses of rocks. Following the passage you'll soon come to a hole covered with straw and branches; a briefcase is in the hole. Use a grenade (or similar) to blow the branches away.
At the center of TaeMoCo Mine you can find a couple of large boulders; one of them has a briefcase on top of it. To reach it, climp up the large "slit" (not sure what such a contraption is called in english - see smaller image in the screenshot).
North of TaeMoCo Mine you can find some large formations of rock. In between them, down a huge gap, lies a briefcase. You can also access this area from the south-east, where you can find an opening in the rocks.
North of the safehouse located in the north-western part of the region you can find a narrow path in between two massive cliffs. Along the eastern side of this path you'll find a small "indent" where you can find a briefcase next to a corpse.
Just outside of the Weelegol area, to the west, you can find a tower of sorts sitting on a cliff. You can't reach it by foot - instead you'll have to use the Hang glider located at Weelegol Village. Fly north-west out of Weelegol and then turn south - stay fairly close to the cliffs and you shouldn't have a problem making it.
North of the Bus Stop, east of Weelegol, you'll find a large area - open plains with trees scattered around. You can find a huge tree here (not sure what it's called) with a hang glider caught at the top; next to the tree lies a briefcase.
Far east of the Bus Stop, right by the edge of the massive cliffs, you can find a small shelter. Behind it is a... pretty weird sight: a hole filled with animal bones, a corpse and what appears to be blood. I'm not sure what to make of it, really; the good news is that there's a briefcase here as well.