The detailed examination by the U. S. Geological Survey of the Idaho Phosphate Reserve has made necessary the mapping of considerable areas occupied by igneous rocks. Such rocks are abundant in southeastern Idaho and present many interesting features. The igneous rocks of the Fort Hall Indian Reservation have already been described.3 In the present paper it is proposed to summarize the igneous geology of the Cranes Flat, Henry, and Lanes Creek quadrangles, which lie in a group 15 miles or more east of the Fort Hall Indian Reservation and are shown in the accompanying map, figure l.4 A more extended account will be presented in a forthcoming detailed report on a larger region, which includes the quadrangles named.
Figure 1.—General geological Map of the Cranes Flat, Henry, and Lanes Creek Quadrangles, Idaho
General Distribution and Character of Rocks
The southeastern corner of Idaho is composed of folded and faulted . . .