National Geochemical Soil Survey of the Conterminous United States

1,323 soil and regolith samples provide a baseline for elemental concentrations across the contiguous United States, collected at approximately one site per 6,000 square kilometers. U.S. Geological Survey research geologists gathered and analyzed these materials from 1958 to 1976 using standardized protocols. This collection represents the only national-scale geochemical dataset from this period with consistent analytical methods.

Use Cases

• Map background concentrations of elements like lead, mercury, or uranium using geospatial sample locations.
• Analyze correlations between soil elements such as calcium, potassium, and iron measured via emission spectrography and X-ray fluorescence.
• Compare organic matter content via total carbon combustion data across different regolith types like desert sands and loess deposits.
• Model regional geochemical patterns for elements like zinc and phosphorus analyzed by colorimetric and atomic absorption methods.
• Establish historical baselines for soil chemistry using standardized data from samples collected at a 20 cm depth.

Strengths

• 1,323 samples analyzed with consistent, documented protocols.
• Covers the entire conterminous United States with a defined sampling density.
• Analyzes over 40 specific elements and compounds using multiple laboratory techniques.
• Samples were specifically chosen from sites in a natural, little-altered condition.

Limitations

• Data collection ended in 1976, making it temporally stale for contemporary analysis.
• Sparse sampling density of one sample per 6,000 sq km limits fine-grained spatial resolution.
• Sample composition mixes true soils with other regolith types like sand dunes, introducing heterogeneity.

Provenance

Source

U.S. Geological Survey, research by Hans Shacklette and colleagues.

Collection Method

Field collection of soil and regolith samples at ~20 cm depth, analyzed in USGS Denver laboratories using spectrography, titration, atomic absorption, and other methods.

Time Range

1958 to 1976

Freshness

null

Geography

Conterminous United States