Mapping the distribution of chemical elements county-by-county

Data from chemical analyses of more than 60,000 stream-sediment and soil samples from all 50 States are now available online courtesy of the USGS.These data will be used to determine naturally occurring levels of chemical elements in stream sediments, and to detect regional chemical anomalies that may affect human health.

This is one phase of a larger project to collect geologic, geochemical, geophysical, and mineral locality information for the entire country. The National Geochemical Survey website includes analyses of samples archived from previous USGS studies, and of samples collected by USGS scientists in collaboration with State and other federal agencies, academia, and industry.

Some of the cool mapping functionality included in this vast resource: view the periodic table of elements, click on any element in the chart for a list of which analytical methods were done and to see national maps showing the distributions by analytical method of each element. The quality of each method for determining the element is also noted (See Table of elements below).

NGS Geochemistry by County
– This section of the report presents maps of several elements on a county-by-county basis in the conterminous states. Included are elements of importance to environmental studies and major elements. The mean and standard deviation of each element was calculated for each county. This was done on the basis of gridded maps (see separate description), which are interpolations of the original point data. The calculations were done using the "zonal statistics" function of the Spatial Analyst extension to ESRI’s ArcMap 8.3 program, which averaged the concentration of each element at each pixel of the geochemical grid contained within each county.

Example: To view concentration of Selenium in US counties:

  • view the national map
  • click on SW USA
  • select San Bernardino County
  • results reveal: Selenium Se (ppm) 0.137 0.084 0.100 1.694

Each window of information appears to lead to more information including maps, downloadable data, etc…

For you data hounds, all datasets and categories are described in detail, with information given on how many samples are contained within each dataset, the density of the geochemical sampling networks, and references to documentation on sampling methods. Also included below are index maps showing the sampling coverage of each dataset, and links to download individual datasets as Excel tables or as "shape files" compatible with GIS software. To access and download data see the following:

A preview of all downloadable data products is offered in order to get a glimpse of the data availability prior to download (see below)