This is Peter from Raney Geotechnical in Sacramento. He was on the farm last week to check our soils for building our green roofed home. We need a soils report to accompany our permit application. Trenches were dug 8 feet deep to see what soil we had to build the constrcution pad and cover the house with. We also had to have the soils inspected for a septic system.
The verdict... It does not get better than this. Two feet deep we have a layer of sandy loam which will compact well for the house foundations and makes the septic design easy. 
More details on the house itself later.
Roots were found 90 inches deep confirming what we already knew that this is some amazing soil.