morning sutra, can not pm my email is m.d.k@comcast.net but will talk about it in both venues. i think it important to LIGHTLY discuss the engineering, soild etc. and you are so right when you mentioned clay as a containment floor.
almost all our sites have been roughed in with dozers equipt with rippers, scraped and then stock piled and then the graders went in and did their thing. some sites we've set up were lined with plastic, and or light rubber mat, many many landfills use a heavy rubber mat to cover the garbage to PREVENT ground water from seeping through it.
looking at the map of southern california the area between Banning cali mesa is flatter than flat. but is pretty close to civilization. the area that is just as flat and quite remote isapple valley all the way to landers. very flat and very dry, and the best thing about this last locale is the property prices are really really cheap. did i say cheap, inexpensive is more like it.