Geologic
Mapping in the western United States Geologic
Mapping in the western United States
Why geologic maps are made and how the are used
Geologic information shown on maps is necessary for countless
reasons, from finding natural resources (water, minerals, oil and gas) to
evaluating potential hazards (earthquakes, landslides, floods, volcanic
eruptions) to describing a fundamental part of the environment that controls
distribution of plants and animals. General purpose geologic maps address
all of these themes, and are an important national data base in the earth
sciences.
From the
National Geologic Mapping
Act of 1992 as codified in Chapter 43, Sections 31a-h of the U.S.
Code. PUBLIC LAW 102-285. 102d Congress. signed May 18, 1992:
"Federal agencies, State and local governments, private industry, and
the general public depend on the information provided by geologic maps to
determine the extent of potential environmental damage before embarking
on projects that could lead to preventable, costly environmental problems
or litigation."
Natural Resources
Groundwater: Geologic maps delineate the likely size and depth of high permeability geologic units such as gravel deposits and porous sandstone. Likely barriers and conduits for groundwater flow, such as clay-rich layers of rock and fault zones, are also identified on geologic maps.
Minable minerals: Geologic maps indicate the presence of metallic and other valuable minerals as well as characteristics of mineralized systems that could indicate mineral deposits at depth.
Energy resources: Geologic maps indicate the presence of coal beds in the rock strata and where the beds extrapolate underground. Maps also indicate likely targets for oil and gas, and are used for targeting these resources by geophysical and drilling methods.
Natural Hazards
Earthquakes: Geologic maps identify the locations of faults that may be susceptible to rupture during earthquakes, and identify the ages of materials cut by those faults, which is an important criteria for establishing the potential danger of the fault.
Volcanoes: Geologic maps show the distribution of young volcanic deposits left by past eruptions of volcanoes, thus providing vital information for predicting the kinds of damage future eruptions could cause.
Landslides: Geologic maps show where mudflows, soil slips, and more destructive massive landslides have occurred. Rock units that are more prone to landslides then can be avoided during future construction of roads and homes.
1997-1998 El Nino: Using geologic information to map potential landslide and debris flow hazards, Pacific coast
Floods: Geologic maps show where deposits from past floods occur, and can be used to zone to avoid future floods.
The URL for this page is: <http://geology.wr.usgs.gov/wgmt/whymaps.html>
Page Maintained by: Dave Miller
Last Modified: 29 June 1998