Thanks for the links!
Only one of my three main garden plots are bad clay, one is sandyish, and one is nice loam. There is a website (see link) with soil types super imposed on satelite images, which shows our property with a line separating two soil types cutting right through this one 30ftx20ft plot. One corner is sand and the rest is clay. How did they get that accurate without tromping over the area?
The clay plot in question has got plenty of organic matter, but mixing is a problem. The area was clay subsoil (i.e. plasticine-like clay mixed with sandstone shards). It was stripped of topsoil during house construction. I dug down 2 ft to the loam and sandy loam sub-subsoil layers and mixed in forest litter as I back filled and then mixed in 8-10 inches of half composted wood chips and leaves into the top layer over the next two years. Two winters ago a heavy cover crop of winter rye was grown on it. The problem is that I don't have a tiller so the soil is a matrix of potting soil-like organic material and gummy blobs. The potatoes will grow well there and dig up easily enough, but it will be a hastle to get the sticky clay off of the tubers
Luckily the nice light topsoil from the property was bulldozed to an adjacent area (which is now the main potato patch).
Here is the site that can get you a satelite picture of your property with soil type.
http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm