Nature and Significance of the Inyo Thrust Fault, Eastern California

Abstract

A major thrust fault, here called the Inyo thrust fault, appears to extend under the northern Inyo and southern White Mountains. The allochthon consists of late Precambrian to Late Ordovician rock near exposures of the thrust fault, but elsewhere rock as young as Pennsylvanian or Permian is exposed. Mississippian rock generally underlies the fault. Chert in the allochthon shows no trace of original structure within many tens of feet of the fault surface, but carbonate rock overlying the fault shows only a thin zone of brecciation and shearing. Overturned folds in the region and offset of Mississippian facies suggest cast-ward movement of the allochthon which contains continuous stratigraphic units for 17 mi across and 55 mi along the mountains. It appears, therefore, that at least an 800-sq-mi block in the northern Inyo and southern White Mountains has moved a minimum of 17 mi eastward along the Inyo thrust fault. The Last Chance allochthon to the east may have been derived from the Inyo–White Mountains allochthon and parts of it may have travelled an additional 20 mi or more eastward. The Harkless Flat allochthon, now preserved on the western flank of the Inyo Mountains, probably has travelled 5 or 6 mi westward from place of origin in the Inyo–White Mountains allochthon. Movement of the Inyo–White Mountains and Last Chance allochthons, and probably the Harkless Flat allochthon, ceased before Middle Jurassic and probably prior to Early Jurassic, as plutons at least 165 m.y. old have not been offset by the thrust faults. These folds and thrust faults in the Inyo and White Mountains form part of a probable Triassic tectonic belt postulated by Burchfiel and others (1970) to extend from southeastern California to Idaho.