Where Can I Get a Geologic Map of My Property?

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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The Short Answer in Most Cases is: You Can't

Here are some reasons why:

• It takes a lot of time and effort to create a really detailed geologic map. Unless your property was of unusual interest, chances are it hasn't been mapped in detail. If it had been, odds are you or a previous owner would have known about it as it happened.
• The sorts of features plotted on geologic maps tend to be large. In the vast majority of cases a geologic map of a single property lot, even a large farm, would contain only a single geological unit; once in a great while a geologic contact (boundary between units) might run across a piece of property. Anything more complicated than that would be extremely rare.
• In many places there just isn't enough information to say much specific about the geology of a single piece of property. In northern Wisconsin, for example, a property might be entirely buried by glacial deposits. The nearest information about bedrock might be an outcrop a mile away on one side and a well a mile away on the other. If the bedrock is the same in both places we are probably safe in assuming it passes under the property as well. If the bedrock is different we can assume there's a contact someplace between the two sites, but there's no way of pinning its location down exactly.

What You Can Get:

Although the odds are very much against your finding a detailed map of your specific property, you can find maps of the surrounding area that include your property:

• The entire United States is covered by topographic maps at scales of 1:24,000 (one inch = 2000 feet, or about 2-5/8 inches per mile). These maps are sold by the U.S. Geological Survey and many private vendors. Indexes are available for each state. A geologist can often tell a great deal about the geology of an area from a topographic map.
• Every state has a geological survey that produces geologic maps. In addition, the U.S. Geological Survey publishes geologic maps, and also produces indexes that include geologic maps published elsewhere, for example, in research journals or graduate theses. Map coverage ranges from very detailed to very sketchy. Only Kentucky is completely covered by geologic maps at 1:24,000 scale, one per topographic quadrangle.
• Much of the U.S., especially agricultural areas, is covered by soils maps. These are often drawn onto aerial photographs so that tiny details are visible. Two warnings are in order. First, soil terminology can be confusing. Second, you may or may not be able to tell much about geology from a soils map. If the soil formed directly from the underlying bedrock, you probably can. If it formed from glacial deposits covering the bedrock, you can't. However, if you're interested in planting the soil, excavating, or slope stability, a soils map may be just what you want.
• Most states collect  well records which are available to the public, and you can get the records from the vicinity of your property. Well drillers vary a lot in accuracy, geological knowledge and record-keeping, many old wells may not have been recorded or the records were lost or misplaced, and wells dug by the property-owners themselves were probably not recorded. In addition state highway departments have test boring records, and state geological surveys often have records and samples from research or exploration wells.

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Created 18 September 1998, Last Update 17 July 2003

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