Leather Oak (Quercus durata durata), preferring the serpentine soil, in the foreground at left. A hardy Blue Oak (Q. douglasii) has found a refuge in the center of the serpentine, at the right. It towers over a smaller evergreen Coast Live Oak (Q. agrifolia var. agrifolia) and other trees, clinging to the same refuge in the otherwise inhospitable serpentine soil. 7:43 am.