Properties and History of an Exhumed Tertiary Oxisol in California

The Ione Formation occurs as isolated exposures along the western foothills of the Sierra Nevada. Presence of an intensely weathered soil profile (an Oxisol) on remnants of the Eocene Ione Formation is direct pedologic evidence for a tropical climate during or subsequent to that time. This is the first detailed description of an exhumed Oxisol in the continental United States. The pedon described here has a thin Al horizon, a red and yellow ironstone horizon over a thick oxic horizon. Below the oxic horizon is a thick deposit of kaolinite clay. The oxic horizon has 11.4% F 2 O 3 , 0.04% organic C, 10.9 meq/100 g clay CEC (Cation Exchange Capacity), 3.5 meq/100 g clay KCl extractable Al, and a pH in H 2 O of 3.3. Kaolinite is the only clay mineral present. This relict soil pedon does not meet criteria below the order level in Soil Taxonomy because of moisture regime limitations. Data such as these illustrate the usefulness of pedology in the study of Tertiary paleoclimatology.