The thesis is a structural and petrographic study of approximately
23 square miles in the Millican SE quadrangle, Deschutes
County, Oregon. The area lies along the Brothers fault zone.
Bedrock in the area is of Pliocene to Recent age and consists
of an older basaltic unit with an associated dacite, a younger dacite,
and a younger basaltic unit. The older basaltic unit and both dacites
have been severely faulted. The younger basaltic unit has filled in
topographic lows and is relatively undeformed.
The dominant faults in the area are en echelon high-angle
normal faults trending N. 40°W. with vertical displacements up to
600 feet. Cross faults with smaller displacements trend N. 45°E.
The normal faults are Reidel and conjugate Reidel shears and are
interpreted as the surface expression of a deep-seated right lateral
displacement. The fault zone displaces units of Miocene to Pleistocene
age and is considered to have been active during that time