Named for exposures on Mount Owen, Teton Co, WY in Northern Rocky Mountain region. Type locality is along trail in South Fork of Cascade Canyon at elev. 8,880 ft 1.9 mi due west of summit of Mount Owen. Is a medium- to fine-grained, light-colored quartz monzonite and associated pegmatite. Consists of 30 to 40 percent quartz, 20 to 30 percent potassium feldspar, 25 to 35 percent plagioclase, 5 percent or less biotite, and a trace of muscovite. Is generally nonfoliated. Dikes, pods, and irregular bodies of pegmatite a few inches to several tens of ft common throughout main mass. Pegmatites contain quartz, oligoclase, microcline, muscovite, and a few garnet crystals. Contacts are irregular. Inclusions abundant near contact. Age thought to be either Precambrian X or Precambrian W. Has an isochron with an age of 2,495 +/-75 m.y.

Source: GNU records (USGS DDS-6; Denver GNULEX).