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Geology - Uncompaghre ' The techtonic uplift of the Uncomphagre Plateau produced a 25 - 30 mile wide and 95 mile long highland, that folded and faulted ' the overlying sediments anticlinally. The southwest margin of the uplift is defined by normal (graben) faults that trend ' obliquely to the Uncomphagre's surface trace. The northwest margin has high angle normal or reverse faults that die out to ' the northwest into folds. The techtonic forces that acted on this area have been active for many hundreds of millions of ' years, and have produced numerous major and lesser uplifts. The localization of these many uplifts is probably due to deep basement faults in the underlying precambrian rock creating ' crustal structural instability that manifests itself in uplifts when compressive forces act on the continent. Underlying the Uncomphagre Plateau is precambrian schist and ' gneiss basement rocks. These rocks are exposed in the deep canyons of the Uncomphagre where rivers and streams have undercut ' the overlying sediments. Lying unconformably on the Precambrian rocks are the permian sandstones of the Cutler Formation. Younger Triassic units of the Moenlcopi, Chinle, Wingate sandstone, and lcayenta formations ' are present above the permian units. Younger still, the units on top of the canyon cliffs in the Uncomphagre Plateau are Jurassic deposits of Entrada sandstone, Summerville and Morrison formations. Finally, the youngest observable units from the lower cretaceous period, are the Burro Canyon, and Dakota sandstone formations which typically cap the canyon walls. The ' youngest resistive units from the upper cretaceous period, that were once present on the Uncomphagre Plateau, have been eroded away, and include the Mancos Shale and Mesa Verde Formations. ~~~ iJ ' 3