Soil samples collected during 2008 were air-dried, disaggregated, and sieved to less than 2 mm. The less-than-2-mm material was crushed to less than150 μm in a ceramic mill and thoroughly mixed to ensure homogeneity prior to analysis by the USGS laboratories for aluminum (Al), calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), sodium (Na), sulfur (S), titanium (Ti), silver (Ag), arsenic (As), barium (Ba), beryllium (Be), bismuth (Bi), cadmium (Cd), cerium (Ce), cobalt (Co), chromium (Cr), cesium (Cs), copper (Cu), gallium (Ga), mercury (Hg), indium (In), lanthanum (La), lithium (Li), manganese (Mn), molybdenum (Mo), niobium (Nb), nickel (Ni), phosphorus (P), lead (Pb), rubidium (Rb), antimony (Sb), scandium (Sc), selenium (Se), tin (Sn), strontium (Sr), tellurium (Te), thorium (Th), thallium (Tl), uranium (U), vanadium (V), tungsten (W), yttrium (Y), and zinc (Zn). The Colorado State University Soil-Water-Plant Testing Laboratory analyzed splits of the less-than-2-mm material for total N, soil pH, electrical conductivity, and sodium adsorption ratio. Rigorous quality control protocols were used throughout the analytical process with two samples having to be reanalyzed by the USGS laboratories for failing to meet the acceptance criteria for accuracy and precision. A statistical summary of soils collected from a depth of 0–5 centimeters (cm) is shown in table 2. In general, the geochemical variation seen for soils of the WLCI study area is similar to that reported for the United States and Canada by Smith and others (2005) and Garrett (2009). Exploratory data analysis, including preparation of histograms, Tukey boxplots, plots of empirical cumulative distribution function, and quantile-quantile plots, was performed on the major- and trace-element data. Multivariate analyses, including principal component analysis and factor analysis, also were conducted. Preliminary geochemical maps were prepared to show the abundance and spatial distribution of each element or parameter and these were compared with other information layers such as geology and ecoregions. Geochemical maps for mercury and organic carbon are shown in figures 8 and 17, respectively. In general, the composition of the soil parent material and climate (amount of precipitation) at a given site were the major controls on soil geochemistry.