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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 20 (1936)

Issue: 10. (October)

First Page: 1308

Last Page: 1328

Title: Dawson and Laramie Formations in Southeastern Part of Denver Basin, Colorado

Author(s): C. H. Dane (2), W. G. Pierce (2)


The Dawson arkose in the Castle Rock and Colorado Springs quadrangles, Colorado, is more than 2,000 feet thick and consists of arkosic conglomerate and sand. It merges northward into the Arapahoe and Denver formations along the foothills of the Front Range, where the beds stand vertically or dip steeply eastward on the west flank of the Denver Basin. The Dawson and Arapahoe formations along this belt overlie with erosional irregularity the finer-grained sands and shales of the Laramie formation, which is coal bearing. In the plains region--on the east side of the basin--where the beds dip gently westward into the basin, the upper part of the Dawson retains its coarsely conglomeratic nature, but the lower part consists chiefly of arkosic sands and dark shales and contains eds of lignitic coal, being thus not much dissimilar to the underlying Laramie upon which it rests with apparent conformity. The Laramie and Dawson formations, however, contain distinctive floras, some additional collections of which are recorded. Identifiable remains of Triceratops have been found in the lower part of the Dawson, but the upper part has not yielded fossils diagnostic of age. The United States Geological Survey now classifies the Dawson as Cretaceous and Eocene (?) in age, instead of Eocene as heretofore.

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