Volume II of the Supplement to the Desert Project Soil Monograph is the second of a number of reports on soils in the Desert Project area. Volume II consists of two chapters, of which the first is a detailed study of a remnant of the Rincon surface and its soils. The Rincon surface is a remnant of one of the oldest basin landscapes in North America, and probably dates from late Pliocene time or earlier. The remnant consists of an ancient basin floor and an adjacent alluvial-fan piedmont, preserved in a bedrock-defended area 600 feet above the Rio Grande flood plain. Chapter 2 focuses on clay mineralogy of the Desert Project and the Rincon study area. It describes clay mineralogy as a function of age, parent material, and depth. It also compiles the narrative clay mineralogy information produced during the period from 1957 to 1972.