Lithofacies analysis of the Tertiary Ojo Alamo Sandstone and related strata in the San Juan Basin indicates that Laramide (Late Cretaceous–early Tertiary) volcanism and uplift north of the present-day San Juan Basin controlled sedimentation patterns of Upper Cretaceous and lower Tertiary rocks. Eight major lithofacies reflect changes in sedimentation that occurred during this time.

The Ojo Alamo Sandstone is characterized in most areas of the San Juan Basin by a pebbly, trough-crossbedded lithofacies. A related channel-form sandstone and shale facies makes up the Ojo Alamo at Mesa Portales. Both lithofacies include both sediment derived from north of the present-day San...