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Regional Geology

The northern and central Black Mountains is characterized structurally by a complex system of high- and low-angle normal faults and related strike-slip faults of mid- to late-Tertiary age. In this region, the interplay of these faults has produced extension of the upper crust on the order of 100% and more, mostly during mid-Tertiary time. In general, east-dipping high-angle normal faults rotate Tertiary volcanic and sedimentary rocks to the east in a domino-like fashion. In many areas these high-angle normal faults merge with depth into zones of low-angle faulting (detachment faults) placing highly extended Tertiary volcanic and sedimentary rocks over Precambrian schist, phyllite, gneiss, and mylonite.