Their History and Ways of Life is the rest of the title. Bird Grinnell was one of the early ones to chronicle the issues between those seeking to "settle" the western frontier and those whose ancestors had occupied it for centuries. An excellent writer, he only slanted his works so slightly (just my take on a lot of his work) ... and my thinking is that he did that only he wanted to "keep" his audience. Little did he suspect that he was writing for posterity.
As I write this I have only one set of the two paperback volumes and a second copy of Volume II. I have found another copy (newer printing then the ones I have) of Vol 1 .. so in theory I have two sets of good quality paperbacks.
Price included both volumes