In the Canyonlands of Utah and Arizona,canyon Walls Often Support

In the canyonlands of Utah and Arizona,canyon walls often support "hanging gardens" in which plants cling to sandstone cliffs and these hanging gardens are typically along shale beds in the sandstone.These areas are deserts,so what might explain these features?

A) The shales hold the water better than the sandstone,so plants preferentially grow in them.
B) The shales form better soils than the sand,so the plants grow there.
C) The shales form aquitards in the sandstone acquifer,trapping groundwater along the shale horizons that helps aid plant growth.
D) The shales are more fractured than the sandstones so the plants have an easier time starting in the shale.