Genesis of a Typic Durixeralf of Southern California

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Abstract
Soils with duripans are common on old marine terraces in San Diego and Orange Counties. The Chesterton series illustrates their complexity. It has a duripan, an argillic horizon which is gleyed in the lower part, and a thick surface horizon having Fe‐Mn nodules. Initial weathering under a warm subhumid climate produced moderate amounts of kaolinite and smectite clay to a depth of several meters. With the onset of a drier climate, a duripan formed protecting the lower part of the former profile from further weathering. Horizons above the duripan later weathered under a cooler, more humid climate to form mostly kaolinitic clays, thus creating a clear mineralogical discontinuity. Simultaneously or subsequently, a relatively intense illuvial process produced a B2t horizon above the duripan. The wet conditions implied by the Fe‐Mn nodules and the mottles are no longer very pronounced. The morphology of the nodules suggests that they are relict features.