The thesis area includes 44 square miles of the Centennial
Range in Beaverhead County, Montana, and Clark County, Idaho.
The rocks exposed in the area range in age from Precambrian
to Recent and have been divided into 23 mapped units. Pre-Belt
metamorphic basement rocks are overlain unconformably by 3,433
feet of Paleozoic strata included in eleven formations. These formations
represent all of the periods of the Paleozoic except the
Ordovician and Silurian.
Nine formations represent all the periods of the Mesozoic and
total approximately 3,127 feet in thickness.
Cenozoic units present in the area are basalts and rhyolites,
landslide debris, glacial deposits, and alluvium.
The major structure of the thesis area is a fault block that is
the result of uplifting and tilting of the east-west trending Centennial
Range during the downwarp of the Snake River Plain in late Pliocene
and Pleistocene time.
No stratigraphic or structural conditions in the thesis area
are favorable for the accumulation and entrapment of oil and gas.
Phosphorite has been mined from the Phosphoria Formation in the