Precambrian metasedimentary rocks of the northeastern Front Range have undergone a long and complex geologic history involving multiple periods of metamorphism, deformation, and intrusive activity. The first event following sedimentation involved deformation which produced large east‐west isoclinal folds and metamorphism in the greenschist facies and possibly higher. It has been impossible to date this first event by radiometric techniques. The second major event was a period of dominantly medium‐ to high‐grade regional metamorphism accompanied by folding and syntectonic intrusions, such as the Boulder Creek granite. Rb‐Sr dating of high‐grade gneisses, pegmatites, and Boulder Creek granite places this event at 1700–1800 m.y. ago. Precambrian metasedimentary rocks younger than 1700 m.y. have not been recognized in the northeastern Front Range. A major period of plutonism is dated at 1390–1450 m.y. ago during which time the Sherman and Silver Plume granites, pegmatites, and basalt and andesite dikes were emplaced. The regional heating of the country rock at this time was effective in lowering most of the Rb‐Sr and K‐Ar mineral ages determined on prebatholithic rocks and probably caused the retrogressive metamorphism which locally affected the gneisses and schists. Post‐batholith faulting and cataclasis, possibly at about 1300 m.y., may have been effective in further reducing some mineral ages.

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