Sage Green accidently finds in a satellite photo the ruins of an old log cabin and a stable in a high mountain valley in the Central Idaho wilderness. Nothing unusual except no entrance exists into that valley.
Mike Hawthorne, on some of his many trips into the past, used to camp and prospect right below that valley without knowing it was there.
With Mike Hawthorne, Sage Green must travel back to find out how to get into that valley, why that cabin and stable exist, and who built them.