(http://www.surevoid.com/assets/soil_maps/us_s.jpg)
(http://www.surevoid.com/assets/soil_maps/legend1.gif)Unit contains abundant clay having high swelling potential
(http://www.surevoid.com/assets/soil_maps/legend2.gif)Part of unit (generally less than 50%) consists of clay having high swelling potential
(http://www.surevoid.com/assets/soil_maps/legend3.gif)Unit contains abundant clay having slight to moderate swelling potential
(http://www.surevoid.com/assets/soil_maps/legend4.gif)Part of unit (generally less than 50%) consists of clay having slight to moderate swelling potential
(http://www.surevoid.com/assets/soil_maps/legend5.gif)Unit contains little or no swelling clay
(http://www.surevoid.com/assets/soil_maps/legend6.gif)Data insufficient to indicate clay content of unit and/or swelling potential of clay (Shown in westermost states only)
To get a closer look at certain areas, you can visit here http://www.surevoid.com/soil_maps/risk_areas_us.php (http://www.surevoid.com/soil_maps/risk_areas_us.php)
There is also the Web Soil Survey site that is interactive. Data not available for all areas; our place in the mountains for example. It's too variable from one valley or ridge to another.
I thought we had a referral topic but all I can find is that it pops up here and there in assorted topics. Refer to...
http://countryplans.com/smf/index.php?topic=10057.0 (http://countryplans.com/smf/index.php?topic=10057.0)
and directly to the WSS itself...
http://websoilsurvey.nrcs.usda.gov/app/ (http://websoilsurvey.nrcs.usda.gov/app/)