The special issue of Rocky Mountain Geology on Proterozoic magmatism of the Rocky Mountains and environs is in two parts: the first was published in fall 1999, and this second part is the first issue of 2000. Whether or not these parts truly span a change in millennia, the turnover from 1999 to 2000 provides an opportunity for reflection on the changes in geological thinking that have taken place in the years since the first geologic descriptions of the Rocky Mountain region.

Systematic geologic descriptions of the Rocky Mountains region began following the Civil War, when national geographical and geological...

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