Most of the large areas of land mines were laid right at the end of the Korean War and over the following few years. I arrived there 17 years after the end of the war, and the mine fields were so old then that the reliability of the mines was poor, at best. I can still remember watching a guy kicking at a piece of something sticking out of the ground, and then we realized that it was one very rusty land mine. Keep in mind that land mines never move up a hill, but sometimes they move down due to erosion. So, we were more likely to find something unexpected at the bottom of a valley below someplace that had been a defensive position back when.
Yes, the parks in the northeast sound like the better bets for mountain travel.