Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

Mountains, and White River uplifts formed in the area of the earlier trough between the
old Front Range and Uncompahgre-San Luis highlands (Tweto, 1980c).
Significant magmatism was initiated during the Laramide orogeny and has
continued through the Tertiary and Quaternary. Most of this Cenozoic magmatism and
associated ore deposits are focused on the northeast-trending Colorado mineral belt (fig.
3). The belt consists of numerous intrusive porphyries and associated ore deposits
initially thought to be predominantly Laramide in age, about 72 to 45 or 40 m.y. (Tweto
and Sims, 1963). By about 1975, mappers found that the Colorado mineral belt
magmatism was more complicated and included two distinct episodes of igneous activity,
a Laramide episode between 70 to 55 m.y. and an Oligocene episode between 39 to 26
m.y. (Steven, 1975), or at least three interspersed populations of intrusions and ore
deposits (Tweto, 1975). Three separate interpretations of the age spans of the three
magmatic populations are in close agreement: the Laramide magmatic pulse from 70 to
50 m.y. (Tweto, 1975 and Cunningham and others, 1994) and 75 to 42 m.y. (Mutschler
and others, 1987); the Middle Tertiary magmatic pulse from 40 to 25 m.y. (Tweto, 1975),
40 to 26 m.y. (Mutschler and others, 1987), and 45 to 25 m.y. (Cunningham and others,
1994); and the Late Tertiary magmatic pulse from 15 to 10 m.y. (Tweto, 1975), 15 to 4
m.y. (Cunningham and others, 1994), and 25 to 0 m.y. (Mutschler and others, 1987).
The record of volcanism associated with the Laramide magmatic pulse is chiefly
in thick sequences of andesitic sediments preserved in the sedimentary basins flanking
the Laramide uplifts (Tweto, 1975). The volcanic sediments and associated flows lie in a
broad northeast-trending belt that generally flanks the Colorado mineral belt, and
contemporaneous Laramide-aged intrusions in the form of stocks, sills and dikes are
concentrated in a narrower belt within the broad volcanic belt (Tweto, 1975). The
Laramide intrusions are focused along the northeast-trending Colorado mineral belt but
also occur in a northwest-trending, transverse sub-belt (fig. 3) that crosses the area of the
northern Sawatch Range (Tweto, 1977; Cunningham and others, 1994). This transverse
sub-belt includes (from NW to SE) the about 62 Ma Fulford stock, the about 59.5 Ma
East Lake Creek stock, the about 61.8 Ma West Cross Creek stock, the about 66.4 Ma
West Tennessee Creek stock, and the about 70.0 Ma (McDowell, 1971; and Wrucke,
1974) Whitehorn granodiorite intrusion (Cunningham and others, 1994). The Twin Lakes
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