Kansas Geologic Maps Robert S
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Kansas Geological Survey Public Information Circular 38 • November 2015 Kansas Geologic Maps Robert S. Sawin, Catherine S. Evans, and John W. Dunham, Kansas Geological Survey Introduction Geology is a part of our everyday lives, usually in ways we don’t think about. Not anticipating the effect our activities may have on our natural surroundings and the effect geology may have on us can be expensive, both economically and environmentally. In Kansas, geologically related disasters cost businesses and individuals millions of dollars each year and endanger lives. Highways sink, buckle, or are displaced; houses slide down hillsides; buildings crack or are infiltrated by groundwater. Understanding the near-surface geology and incorporating geologic evaluations Pba into planning processes can prevent many structural and environmental problems and keep people safe. Geologic maps, the principal source of information about the geology and natural resources at or near the surface, are essential for evaluating natural resources, making economic decisions, and guiding public policy. The Kansas Geological Survey (KGS) makes basic geologic information about the state available to the public through its county geologic mapping program. This circular explains what geologic maps are, how they are made, what they are used for, why they are valuable, and where to obtain them for Kansas. Figure 1—Portion of the Tallgrass Prairie National Preserve geologic map (Chase County). The What is a Geologic Map? bedrock geology includes layers of limestone—some with embedded chert, or flint—mudstone, and Geologic maps (fig. 1) depict bedrock— shale representative of the Flint Hills. Colors in the key represent rock units shown on the map. the solid rock at the Earth’s surface or directly beneath the vegetation, soil, and bedrock through erosion are considered carried in by water in recent geologic thin deposits of unconsolidated material part of the cover and are generally not time and deposited on flood plains or collectively called “cover.” Limestone, shown on geologic maps. However, in in stream valleys. Loess (pronounced sandstone, and shale are common types areas where bedrock is covered with in various ways but often rhymed with of bedrock in Kansas. thick and widespread deposits of sand, “us”) is a thick layer of unstratified Soils and thin, unconsolidated surface gravel, clay, silt, and other materials sediment—mainly silt derived from or near-surface materials derived from carried in by wind, water, and ice, glacial materials and deposited by the the deposited material instead of the wind. Sand dunes are formed from Terms in bold are defined in the glossary. deeper bedrock is depicted on the windblown material—mainly sand map. Sediment deposits up to tens of derived from alluvial deposits. Glacial feet thick in Kansas include alluvium, drift is composed of rock fragments and loess, sand dunes, and glacial drift. sediment—from massive boulders to Alluvium consists of unconsolidated silt—eroded, transported, and deposited sand, gravel, clay, and silt that has been by glaciers or glacial meltwater. Each geologic map graphically • Planning transportation and utility Making Geologic Maps portrays the type, age, and distribution routes Geologic maps are made by scientists of surface or near-surface rock units • Planning for urban growth and with the training and experience in a state, county, region, or area of recreation needed to identify rocks at the surface; interest, such as the Tallgrass Prairie • Siting and excavating lakes and make inferences about the near- National Preserve in the Flint Hills in ponds surface geology underlying the cover Chase County shown in fig. 1. Each • Selecting sites for landfills, treatment of soil, vegetation, and thin deposits unit is identified and named based facilities, and underground storage of unconsolidated materials; and on distinctive characteristics that can tanks graphically depict the bedrock as it be mapped over large distances. For • Planning land use and evaluating would appear without the cover. example, the Wreford Limestone, land-use proposals To create a geologic map, one or named after the unincorporated • Assessing, exploring, developing, and more geologists start by assembling community of Wreford in Geary managing natural resources existing geologically related materials County, is found throughout the Flint • Developing and protecting for the mapping area. These include Hills, including in the preserve and in groundwater resources aerial photographs, remote sensing roadcuts along Interstate 70. Attributes • Writing government regulations data, measured stratigraphic sections, that help distinguish Wreford • Carrying out basic earth-science highway construction plans, shallow Limestone from other rock units research core and borehole records, geologic include its thickness and the presence Engineers, architects, developers, cross sections, water-well records, soil of chert, also called flint. and city planners, in particular, use surveys, and published books, articles, Lines, symbols, and colors are geologic maps to assess the feasibility and maps. The information from these used on a geologic map to show the of construction and development at a sources is used to locate rock units and relationship between rock units and specific site to avoid safety, health, and geologic features during fieldwork and to accentuate the three-dimensionality financial risks. When the location of a to interpret data collected in the field. of the bedrock geology (fig. 2). Folds, floodplain or landslide hazard is not During fieldwork, geologists faults, fractures, and other geologic considered during urban development, systematically drive and walk along features created by deformation and a preventable disaster could occur. If roads, streams, and hillsides to examine displacement of the rocks are shown building construction is not adapted to surface materials and locate outcrops— where they would appear if the the local geology, concrete may crack, the portions of rock units exposed at overlying soil were stripped away. Lakes, foundations may shift, basements the Earth’s surface. Outcrops can occur rivers, roads, towns, and other natural may flood, and large structures may naturally, for example where rock has and cultural features are included to help even collapse. Dam failures due to eroded along streams and cliffs, or they users pinpoint locations. A rock column unstable geology endanger downstream can be human-made, such as those in showing the names and descriptions of communities and farms. quarries and roadcuts. Geologists will each rock unit and the order in which On a smaller scale, a landowner can examine each rock exposure in detail they were deposited over time (fig. 3) use a geologic map when choosing a to identify the rock units and geologic is included on each map. The KGS also site to drill a domestic water well or contacts, which are the boundaries provides a general description of the construct a farm pond. For example, a between the rock units based on the type local geology and water and mineral pond built in shale containing clay that and age of the rocks (fig. 6). resources. Geologic maps often have a forms a tight seal should hold water Understanding the stratigraphy, geologic cross section that represents a while one built in sand and gravel, or sequence of rock layers, is an vertical slice of subsurface rock layers on porous sandstone, or on fractured important part of the mapping process. through a designated area (fig. 4). limestone will likely drain. Rocks beneath the surface or visible The information on geologic maps in outcrops are layered in the order in Benefits and Uses is helpful, and often essential, for any which they were deposited, unless they Compiled from the most comprehensive project that will affect or be affected by were displaced by faulting, folding, or information available—including first- the type and structure of the underlying other processes. Bedrock type varies hand field observations and previously bedrock, water resources, and other from one place to another, even in a published maps and reports—geologic natural resources. Assessing the geology small area, because geological processes maps and the digital data associated of a site before altering it in any way (deposition, erosion, etc.) are rarely with them are the best starting point increases the chance of foreseeing uniform across a mapping area. for any project concerning the use, and avoiding construction failures, To assure consistency from one conservation, or study of natural environmental damage, and natural county to the next, layers of bedrock are resources. They can be useful when disasters. Once a problem has occurred, identified according to long-established • Evaluating landslides, earthquakes, such as the landslide that took out a boundaries and names (fig. 3). Unit and sinkholes section of McDowell Creek Road south boundaries usually represent a change • Designing and constructing of Manhattan in 1995 (fig. 5), geologic from one predominant rock type to highways, bridges, and tunnels maps are used to evaluate the surface another, such as shale to limestone. In • Building schools, sports stadiums, geology, plan reconstruction, and avoid Kansas, the thickness of each unit ranges skyscrapers, and other structures future problems. from a few feet to tens of feet. Geologists 2 Figure 2—Portion of the Saline County geologic map southwest of Salina, which includes Coronado Heights, the Smoky