Some areas in Southern California in particular will have layers of different sediment types throughout a yard. That said many housing developments are on backfill which could be sourced from a construction project miles away with completely different substrate. That said, I agree to an extent regarding sandy loams, as you get good drainage and excellent root development, but there are significant downsides to consider.
Gophers stay active in tunneling in silty or sandy loam soils long into the summer, with no apparent signs of activity above ground. In areas where clay composes higher percentages of the soil, the soil sets up much harder, also causing the stated issues regarding root penetration.
Additionally, the shallow clay soils particularly on very steep sloped hills can retain significant moisture throughout extended drought conditions. These benefits should not be overlooked, in addition, heavier soils allow nutrients to be retained, where looser soils often allow nutrients to be leached.
Becoming familiar with your particular growing environment should be considered as it will guide your decisions when setting up a grove.