Investigation of the structure of the desert ranges which lie between the Wasatch and the Sierra and extend southward into California is no easy task. In the past different views have been held, some seeing in them a series of parallel folds in which the anticlines protruding above the surface formed the ranges, while others considered them a series of unfolded blocks, broken by parallel faults, and upheaved along these faults so as to form ridges. Besides these entirely opposed theories a compromise view has been entertained, namely, that the ranges were first folded and subsequently broken into blocks by faults and upheaved into mountains. Even in this compromise there has been great diversity of opinion as to the relative importance of the two chief agents in mountain-building. King,* for example, considered that folding has been most potent, while Russell† believed that the ranges as they now stand . . .