Geology and Soil

Stone and Soil

geology  | the science that deals with the earth’s physical structure and substance, its history, and the processes that act on it; the geological features of an area: the geology of the San Francisco Peaks volcanic field.

As bedrock crumbles and plant material decomposes, soils develop. Our soils are generally alkaline, shallow, and stony because both rocks and plants break down very slowly in our dry climate. Neighborhoods in floodplains—including Downtown, Townsite, Southside, NAU, Bow and Arrow, Foxglenn Park, and Continental—have deeper soil than most other areas, but it tends to be heavy in clay. Areas east of town have cindery soils, which have a unique texture with both advantages and disadvantages for gardening.

  • See Geology Map and Rock Types for locations and descriptions of parent rock (bedrock) types in the Flagstaff area.
  • See Landscape and Geologic History by Wayne Ranney for a narrative of local geology.
  • See Introduction to Soil for an explanation of how our soils affect the growth of plants.
  • See Rio de Flag and Walnut Creek under Plants and Animals for information and a map of these watersheds, which have carved features into the landscape that provide vital habitat for native plants and movement corridors for wildlife.
  • See Improve Your Soil under our Advice column for suggestions on how to improve the soil in your garden.