BRIDGER FORMATION--Greenish-gray, olive-drab, and white tuffaceous sandstone and 
     claystone; lenticular marlstone and conglomerate.  Tb
CROOKS GAP CONGLOMERATE--Giant boulders of granite in arkosic sandstone matrix. 
     Reynolds (1976) considers age of eastern exposures to be Oligocene(?).  Tcg
VOLCANIC CONGLOMERATE--Dark-brown to black conglomerate, poorly bedded, composed 
     chiefly of basalt clasts in a basaltic tuff matrix.  Tv
ALKALIC INTRUSIVE AND EXTRUSIVE IGNEOUS ROCKS (AGE ABOUT 44 Ma)-
     Light- to greenish-gray porphyry.  Tai