The Carter family story I have is that it was Engine 143 that Sara was singing when AP saw her and fell in love-- which makes a lot more sense, since the Great Divide is one that Sara wrote around 1950 or so when she was taking the transcontinental RR back and forth from Angels Camp down to see her children who still lived (and still live!) around Maces Spring VA. It's one of the last authentic Carter Family songs and to me it's one of the best.