Generalized Surficial Geologic Map of the Denver 1 degree x 2 degree Quadrangle, Colorado

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 and Quaternary geology. Geologic hazards (e.g.,
landslides, swelling soils, heaving bedrock, and flooding) known to be located
in, or characteristic of some mapped units, were identified.

Surficial deposits in the quadrangle partially record depositional events of
the Quaternary Period (the most recent 1.8 million years). Some events such as
floods are familiar to persons living in the area, while other recorded events
are pre-historical. The latter include glaciation, probable large earthquakes,
protracted drought, and widespread deposition of sand and silt by wind. At
least twice in the past 200,000 years (most recently about 30,000 to 12,000
years ago) global cooling caused glaciers to form along the Continental Divide.
The glaciers advanced down valleys in the Front Range, deeply eroded the
bedrock, and deposited moraines (map units tbg, tbj) and outwash (ggq, gge). On
the plains (east part of map), eolian sand (es), stabilized dune sand (ed), and
loess (elb) are present and in places contain buried paleosols. These deposits
indicate that periods of sand dune deposition alternated with periods of
stabilized dunes and soil formation.

Thirty-nine types of surficial geologic deposits and residual materials of
Quaternary age are described and mapped in the greater Denver area, in part of
the Front Range, and in the piedmont and plains east of Denver, Boulder, and
Castle Rock. Descriptions appear in the pamphlet that accompanies the map.
Landslide deposits, colluvium, residuum, alluvium, and other deposits or
materials are described in terms of predominant grain size, mineral or rock
composition (e.g., gypsiferous, calcareous, granitic, andesitic), thickness of
deposits, and other physical characteristics. Origins and ages of the deposits
and geologic hazards related to them are noted. Many lines between geologic
units on our map were placed by generalizing contacts on published maps.
However, in 1997-1999 we mapped new boundaries, as well. The map was projected
to the UTM projection. This large map area extends from the Continental Divide
near Winter Park and Fairplay ( on the west edge), eastward about 107 mi (172
km); and extends from Boulder on the north edge to Woodland Park at the south
edge (68 mi; 109 km).

Compilation scale: 1:250,000. Map is available in digital and print-on-demand
paper formats. Deposits are described in terms of predominant grain size,
mineralogic and lithologic composition, general thickness, and geologic
hazards, if any, relevant geologic historical information and paleosoil
information, if any. Thirty- nine map units of deposits include 5 alluvium
types, 15 colluvia, 6 residua, 3 types of eolian deposits, 2
periglacial/disintegrated deposits, 3 tills, 2 landslide units, 2 glaciofluvial
units, and 1 diamicton. An additional map unit depicts large areas of mostly
bare bedrock.

The physical properties of the surficial materials were compiled from published
soil and geologic maps and reports, our field observations, and from earth
science journal articles. Selected deposits in the field were checked for
conformity to descriptions of map units by the Quaternary geologist who
compiled the surficial geologic map units.

FILES INCLUDED IN THIS DATA SET:
>denvpoly: polygon coverage containing geologic unit contacts and labels.
>denvline: arc coverage containing faults.
>geol_sfo.lin: This lineset file defines geologic line types in the
> geologically themed coverages.
>geoscamp2.mrk: This markerset file defines the geologic markers in the
> geologically themed coverages.
>color524.shd: This shadeset file defines the cmyk values of colors
> assigned to polygons in the geologically themed coverages.