The underlying soil is decomposed granite going 10’s of meters down. It was once under coastal marine layers and consequentially contains Calcium. On top of the DG is 5" to 10" of greyish coastal clays, and on top of those were 5" to 10" of terrestial clays. When I purchased this property in April 2013 the rear of the property sloped down at 45° for 10’ and then extended another 10’ to the property behind me. I built a set of retaining walls and brought the property back up to “level” – although there is a 1° to 2° slope for drainage. During this phase there was extensive grading which moved most of the top clays to the rear (as fill) plus another 150 cu.yd. of DG fill trucked in from a nearby construction project.
So in places on the surface the tan colored DG has traces of the grey clays – some left over from construction and some from excavation of tree holes.
Here’s an aerial picture of the property during construction. The green plants in the photo are my entire collection in pots!
