Digital database of the previously published geologic map of the greater Denver area, Front Range Urban Corridor, Colorado

This digital map shows the areal extent of surficial deposits and
rock stratigraphic units (formations) as compiled by Trimble and
Machette from 1973 to 1977 and published in 1979 under the Front
Range Urban Corridor Geology Program. Trimble and Machette
compiled their geologic map from published geologic maps and
unpublished geologic mapping having varied map unit schemes. A
convenient feature of the compiled map is its uniform
classification of geologic units that mostly matches those of
companion maps to the north (USGS I-855-G) and to the south
(USGS I-857-F). Published as a color paper map, the
Trimble and Machette map was intended for land-use planning in the
Front Range Urban Corridor. This map recently (1997-1999) was
digitized under the USGS Front Range Infrastructure Resources
Project. In general, the mountainous areas in the western part of
the map exhibit various igneous and metamorphic bedrock units of
Precambrian age, major faults, and fault brecciation zones at the
east margin (5-20 km wide) of the Front Range. The eastern and
central parts of the map (Colorado Piedmont) depict a mantle of
unconsolidated deposits of Quaternary age and interspersed
outcroppings of Cretaceous or Tertiary-Cretaceous sedimentary
bedrock. The Quaternary mantle comprises eolian deposits (quartz
sand and silt), alluvium (gravel, sand, and silt of variable
composition), colluvium, and a few landslides. At the mountain
front, north-trending, dipping Paleozoic and Mesozoic sandstone,
shale, and limestone bedrock formations form hogbacks and
intervening valleys.