State Geologic Maps

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Index Map

Gravity and Magnetic Maps of the States

Click on the desired state to view the map. Scale on all maps is one pixel = one kilometer

Canada and the Caribbean

Geologic Map of Southern Ontario
Geologic Map of East-Central Ontario (north of Lake Huron)
Geologic Map of West-Central Ontario (north of Lake Superior)
Geologic Map of Ontario: James Bay
Geologic Map of Northwest Ontario
Geologic Map of Maritime Provinces
Geologic Map of Newfoundland
Geologic and Bouguer Gravity Map of the Grand Banks and Flemish Cap
Geologic Map of Cuba
Geologic Map of Hispaniola and Puerto Rico

About the Maps Washington Oregon

The maps were generated from U.S. Geological Survey Digital Data Series DDS-11, Release 2, 1998, by Paul G. Schruben, Raymond E. Arndt and Walter J. Bawiec. This is a CD containing a digitized version of the Geology of the Conterminous United States at 1:2,500,000 Scale, 1974, by P.B. King and H. M. Beikman. Maps of the individual states have been extracted and rectified with north up.

The CD contains a number of file types, including a color image viewable at one pixel = 500 meters. However, close comparison of the digitized map compared to the original paper map, as well as comparison to more detailed maps, shows that the map cannot be reliably used at such a scale. The viewing scale of one pixel per kilometer is probably the largest scale that can be reliably used, and caution should be used in applying the maps at kilometer scale.

Coloring has been maintained fairly similar to the paper USGS map with some exceptions. Within periods, colors mostly grade from dark at the bottom to light at the top. The middle color is used generically for undivided periods. For sedimentary units, coloring is as uniform as possible across the map, with a few ad-hoc variations for areas where extra subdivisions are required. The principal exception is that I insist granite is pink on a geologic map and other igneous rocks should be red or orange. Igneous and metamorphic rocks are colored using shades that contrast with other rock units, and vary in usage in the Appalachians (Paleozoic), Midcontinent (Precambrian) and far West (mostly Mesozoic and Cenozoic). Each map has its own color legend. 

How the Maps Were Made

The primary data set on the CD is an ArcView file. Arcview permits images to be exported in several formats, including WMF (Windows Metafile). Maps of individual states were saved as WMF files (either of the two options presented will work). Metafile is a generic vector file format used by Windows applications. The virtue of vector files is that they can be scaled and rotated without loss of information.

The WMF file must then be imported into an application that can read it. Microsoft Word can import these files. 

Now you have to get the picture into a drafting program. I use Paint Shop Pro; the procedures will vary depending on the program. After copying the image, I went to Paint Shop and pasted it. A small dialog box came up with the size of the image in pixels. I pasted the image into Paint Shop, then determined the desired scaling factor. Typically, a degree of latitude in the imported image was 85 pixels, but to get a scale of one kilometer per pixel, a degree should be 40,000/360 = 111 kilometers. I deleted the image and re-imported it, multiplying the pixel dimensions by 111/85 to get the proper scale. The exact procedures will depend on the desired scale and the drafting program used.

Legend

Marine refers to well-stratified rocks mostly (but not entirely) of marine origin. Eugeo refers to eugeosynclinal rocks, that is, deep-water sedimentary rocks of continental slope or trench origin. Other headings are self-explanatory.

There are about 160 lithologic units on the Geologic Map of the United States by King and Beekman, counting units with metamorphic overprint. The 256 colors on an 8-bit color palette are more than enough to show these, but many of the colors are very hard to distinguish by eye. Colors were chosen to minimize confusion as much as possible, but inevitably there will be adjacent colors that are hard to tell apart. To improve contrast, a few colors have been duplicated for units widely separated in space and time. For example, colors for early Paleozoic volcanic units (found only in the Appalachians) have also been used for some units in the far West.

Some periods are divided in some locations and undivided in others. Undivided periods generally use the middle color for the period. In practice this seems to result in little confusion. If adjacent units are other divisions of the period, the color represents a subdivision. If adjacent units are different periods, the unit is undivided.

Symbols

Periods

Units of undivided age

Combinations of symbols refer to transitional or undivided units. For example DS refers to undivided Devonian and Silurian rocks.

Prefixes

Suffixes


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Created 23 July 2001, Last Update 02 May 2013

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