The Copper Hill area of the NW Gillis Range, Mineral County, NV was affected by
multiple structural events. Compression during the Mesozoic resulted in at least two
phases of tight folding. Two major structural events occurred during the Tertiary. These
are Basin and Range east-west extension and subsequent Walker Lane northwestsoutheast
strike slip faulting. Basin and Range extension occurred before 23 Ma, resulting
in normal and left-lateral strike slip faults. This deformation regime caused two
different rotations in the area. Normal faults within the eastern Copper Hill area cut and
impart a 25° northeast rotation on both the Oligocene-Miocene tuff and Mesozoic rocks.
Range-front normal faulting appears to have caused regional rotation ~28° southwest.
Walker Lane faulting began after 23 Ma and has continued to the present. Walker Lane
faults show right lateral strike slip movement and typically trend northeast to northnortheast
in the Copper Hill area. The transition from Basin and Range to Walker Lane
faulting includes reactivation of pre-existing faults and development of new faults.