The U.S. Geological Survey (USGS) is developing SPARROW models (SPAtially
Related Regressions On Watershed Attributes) to assess the transport of contaminants (e.g., nutrients) through the Pacific drainages of the United States (the Columbia River basin; the coastal drainages of Washington, Oregon, and California; the Klamath River basin; the Central Valley of California, and the west slopes of the Sierra Nevada Mountains). SPARROW relates instream water quality measurements to spatially referenced characteristics of watersheds, including contaminant sources and the factors influencing terrestrial and aquatic transport. Cattle manure applied to grazing land is a potential source of nutrients delivered to streams. The spatial data set “Application of manure nitrogen generated by grazing cattle to grazing land within the Pacific drainages of the United States (2012)” represents an estimate of the amount of manure nitrogen generated by grazing cattle in 2012 that was applied to grazing land within the counties in which those cattle were located. This data set was created by disaggregating the manure nitrogen generated by grazing cattle within each county to the potential grazing land within that county.