FIGURE 6. Cross sections across the San Juan Basin from northwest to southeast showing how differing use of nomenclature of Fruitland and Kirtland Formations affects ideas of a pervasive unconformity at the base of the Ojo Alamo sandstone (adapted from Fassett and Hinds. 1971, plate 2). A, Nomenclature of Fassen and Hinds (1971) suggesting angular unconformity at the base of the Ojo Alamo Sandstone because of progressive southwestward truncation of the Farmington and Dena-zin Members of the Kirtland Formation and the Kirtland Formation undivided. B. Nomenclature of this report, indicating that there is no angular unconformity at the base of the Ojo Alamo Sandstone because the Kirtland Formation is continuous across the basin and most depositional thinning is caused by the pinching out of the Farmington Member (after Hunt, 1984, plate 1). Abbreviations are: H. Huerfanito Bentonite Bed; KF. Fruitland Formation; KKB, Bisti Member of Kirtland Formation; KKD, De-na-zin Member of Kirtland Formation; KKF. Farmington Member of Kirtland Formation; KKHW, Hunter Wash member of Kirtland Formation; KKU. Kirtland Formation undivided; KPC, Pictured Cliffs Sandstone.