So my answer for you, in line with previous replies no less, is one word: clay. I'm in northern CA and know a guy who achieved it on his hillside property. I also see things like it happening all the time in my line of work as an ecological landscaper (with some suburbaniculture on the side): where there is heavy clay (literally almost everywhere in northern CA) and an excess of water, it will pop up wherever it can downgrade, sometimes only inches below the height of percolation and sometimes a few tens of feet. It really all depends on soil texture. But it is, indeed, very possible — *in heavy soils that catch water*
