USDA Web Soil Survey
a great tool that may be useful: http://websoilsurvey.nrcs.usda.gov/app/. You can learn a great deal about the soil at specific locations *before* you take soil samples (or not) because the NRCS may have already sampled the soil for you. They've pretty much mapped the whole country.
This tool not only give you information about the chemical, physical, and structural attributes of your soil, but also information about uses, and other interesting features. On very valuable feature,was information about the soil horizons - both depth and structure. One could find out how deep it is to a restrictive layer, if one exists.