Fig. 5: Conceptual model of the impact of climate upon the development of secondary material within the examined Fe-rich soils.

In the hot and arid climate at Pickhandle Gulch, the only observed accumulations of non-parent material at this site can be attributed to detrital input of dust-borne particles. In the relatively warm and wet Mediterranean climate of the Klamath Mountains, the formation of Fe-oxyhydroxides occurs rapidly (within ~12 ka), with the development of smectites observed in older soils (25–50+ ka), with relatively limited in situ formation and persistence of amorphous material. In the subarctic climate of the Tablelands, amorphous material (both Fe- and Si-containing) forms rapidly and is the predominant secondary material in all examined soils. Smectite development was not observed in any measured soil in the Tablelands.