This scarce, separately issued large-format map shows remarkable geological detail of the state. It was issued in the same year as the similar-sized companion map entitled Topographic Map of Colorado. The map served as a much-needed update to Hayden's 1877 Geologic Map of Colorado and incorporated both published and previously unpublished geological information provided by the U. S. Geological Survey and Colorado Geological Survey. The state's varied geology is revealed through an extensive legend at right revealing 68 different color/pattern combinations including 37 sedimentary formations and 12 types of igneous rocks. Among state geologic maps, it is unusual because it served as a kind of "progress map," superimposing the most recent and more detailed geological mapping performed mainly by the U. S. Geological Survey (shown by numbered areas with red boundaries), onto the older and reconnaissance-level mapping done by the Hayden survey where new information was not yet available. Drawn by H.C. Woods on a detailed scale of 8 miles per inch and prepared by Russell George of the Colorado State Geological Survey. Backed with old linen.

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Condition: B

A colorful example on a lightly toned sheet that has been backed with linen. There are numerous tiny edge chips and small tears in the margins, along with two large chips in the corners of the top margin. Signed in a blank area of the image at bottom right.