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Generalized Surficial Geologic Map of the Denver 1�x2� Quadrangle, Colorado


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2013-05-16 14:06:38


Thirty-nine types of surficial geologic deposits and residualmaterials of Quaternary age are described and mapped in the greaterDenver area, in part of the Front Range, and in the piedmont andplains east of Denver, Boulder, and Castle Rock. Descriptionsappear in the pamphlet that accompanies the map. Landslidedeposits, colluvium, residuum, alluvium, and other deposits ormaterials are described in terms of predominant grain size, mineralor rock composition (e.g., gypsiferous, calcareous, granitic,andesitic), thickness of deposits, and other physicalcharacteristics. Origins and ages of the deposits and geologichazards related to them are noted. Many lines between geologicunits on our map were placed by generalizing contacts on publishedmaps. [...]


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The map and descriptions offer information that may be used for:land-use planning (e.g. selecting land fill sites, greenbelts,avoiding geologic hazards), for finding aggregate resources(crushed rock, sand, and gravel), for study of geomorphology andQuaternary geology. Geologic hazards (e.g., landslides, swellingsoils, heaving bedrock, and flooding) known to be located in, orcharacteristic of some mapped units, were identified.Surficial deposits in the quadrangle partially record depositionalevents of the Quaternary Period (the most recent 1.8 millionyears). Some events such as floods are familiar to persons livingin the area, while other recorded events are pre-historical. Thelatter include glaciation, probable large earthquakes, protracteddrought, and widespread deposition of sand and silt by wind. Atleast twice in the past 200,000 years (most recently about 30,000to 12,000 years ago) global cooling caused glaciers to form alongthe Continental Divide. The glaciers advanced down valleys in theFront Range, deeply eroded the bedrock, and deposited moraines (mapunits tbg, tbj) and outwash (ggq, gge). On the plains (east part ofmap), eolian sand (es), stabilized dune sand (ed), and loess (elb)are present and in places contain buried paleosols. These depositsindicate that periods of sand dune deposition alternated withperiods of stabilized dunes and soil formation.

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