This study defines the distribution, grade, and quality of diatomite at the White Cliffs diatomite deposit, Mammoth, Arizona. The deposit is hosted in a lacustrine facies of the Quiburis Formation, a Miocene to Pliocene basin-fill sediment of the lower San Pedro Valley. The lake bed sediments are divided into three informal members, the Redington, White Cliffs, and Gust James. Diatomite is found only in the White Cliffs member, and three potential ore zones are defined.