The Colorado Front Range is the largest structural and topographic element in the eastern Rocky Mountains. Its axis parallels the northerly trend of the mountain front through central Colorado. Two additional trends are recognized in the Colorado Rockies. A northwesterly zone of uplifts extends from the Apishapa arch to the Uinta Mountains. A similar, but more vaguely expressed, northeasterly zone localizes a belt of Laramide igneous intrusives. These regional trends constitute the tectonic framework within which the Front Range evolved.

Fragmentary data on the structure of the basement complex suggest a probable relation between Precambrian and later structures. Paleozoic and Mesozoic crustal movements and sedimentation accentuated and modified Precambrian structural trends. In general the sedimentary cover was relatively thin, but locally thicknesses exceed 15,000 feet. Certain positive elements may have persisted from ancestral Rocky Mountain time into the Cretaceous.

Associated with the northeast-trending belt of Laramide intrusives in the central part of the Front Range are northeast- and northwest-trending steep faults that appear to form a conjugate system of shears. Recurrent movements along these faults were complex and displacements noted along the margins of the range are in places opposite to those observed in the crystalline core. Along the northeast flank of the range, the northwesterly faults cut the sedimentary rocks and produce en echelon folds.

Except along the northeast flank, the Front Range is bounded by reverse faults and thrusts that dip toward the mountains. The range was wedged upward along these faults, and adjacent sedimentary basins were depressed during Laramide time. Thrusting was most prominent adjacent to and within those areas which had received the greatest thicknesses of pre-Laramide sediments.

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