Named for exposures in lower parts of cliffs on northwest side of Moose Creek 1.9 mi S 78 deg E of Owl Peak in Ranger Peak 7 /12 min quad, Teton Co, WY in Northern Rocky Mountain region, the type locality. Composed of medium- to coarse-grained, strongly foliated nonlayered biotite- and hornblende-bearing gneiss of quartz monzonite composition. Forms several large concordant bodies in northern Teton Range. Is in contact with layered biotite and amphibolite gneisses. Contains amphibolite layers several in to several hundred ft thick. Where amphibolite is absent, contact with layered biotite gneisses are gradational over a few tens of hundreds of ft, and Webb Canyon is finer grained and rudely layered near contact. May have been derived from felsic volcanic rocks, flows, or tuffs interlayered with flows or sills of basalt that were metamorphosed to produce amphibolite layers. Rb-Sr data show an isochron with an age of 2,875 +/-150 m.y., or Precambrian W age.

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