Named in honor of Robert S. Dietz, geologist and professor emeritus at Arizona State University. Dietz is a pioneer in the study and recognition of terrestrial impact structures, and he was one of the early proponents of the impact origin of the craters of the moon. He championed the concept of shatter cones as diagnostic features of terrestrial impact structures and discovered shatter cones at many of the impact sites now known. On the basis of evidence from shatter cones, Dietz revived the hypothesis of impact origin of the great Vredefort Ring of South Africa and proposed an impact origin for the Sudbury Basin, Ontario. (M 18461) _ _.