The Antelope coal mine in Wyoming’s Powder River Basin is one of the biggest in the country. Union Pacific and BNSF share a 4-track mainline through the basin to serve all the coal mines in the area. This is the largest coal producing area in the country. The Antelope mine has it’s own loop track through the loading facility to get trains in and out as quickly as possible and back out on the mainline. Here’s an old picture of the area. As one can see, this is a busy area and not a place for a runaway locomotive!
http://www.railpictures.net/viewphoto.php?id=398006
http://www.railpictures.net/viewphoto.php?id=261462