Abstract

The northern Madison Mountains consist of at least three east-west-trending, elongate fault blocks that achieved most of their elevation by Eocene time. The blocks were either (1) initially downfaulted, eroded of all Mesozoic and most Paleozoic strata, and then uplifted, or (2) uplifted without downfaulting, but varied in relative rates of uplift. A subdued topography developed on metamorphic rocks. Fault blocks were buried by a northward-sloping plain of Oligocene-Miocene sediment. Consequent streams on the plain were diverted by highlands of the central fault block. Stream courses were influenced by the slope of the plain, barriers to northerly drainage, exhumed Tertiary valleys, and lowering of base level brought about by the Madison River. Tertiary topography was partially exhumed.

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