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Van Tuyl Lecture: Steve Keller, Colorado Geological Survey
November 1, 2018 @ 4:00 pm - 5:00 pm
Steve Keller, Colorado Geological Survey
241 Berthoud Hall, 4PM
Topic: Investigations in the late Eocene Castle Rock Conglomerate, 1869-2018
Abstract: The late Eocene Castle Rock Conglomerate (Tcr) has been of interest to geologists, starting in the late 19th century and continuing to the present day. The formation caps the prominent Castle Rock butte north of the Town of Castle Rock, and is especially well exposed in the cliffs, ledges, and flat outcrops at Castlewood Canyon State Park south of Franktown. It lies on the west flank of the southern part of the Denver Basin, occurring in a swath of outcrops between 3 and 10 km in width, extending ~63 km southeast from near Sedalia in Douglas County to the rim of Bijou Basin in Elbert County. The appearance of the unit is striking, with massive cobble and boulder-rich gravel layers, multiple horizons of very large trough cross-beds, sets of planar cross-beds, slump blocks of rhyolitic tuff, cut-and-fill structures, and some fossilized logs and vertebrate bones. The Tcr is thought to be largely deposited by torrential flooding in a southeast-flowing braided stream system in which velocities could have reached 10 m/s. We will present a chronology of geologic investigations in the Castle Rock Conglomerate, illustrate and explain its important features, and highlight recent research that the Colorado Geological Survey has conducted in this unit.