In later work he became interested in meteorite impacts, was the first to recognize the Sudbury Basin as an ancient impact event, and discovered a number of other impact craters. He championed the use of shatter cones as evidence for ancient impact structures. He received the Walter H. Bucher Medal from the American Geophysical Union in 1971, the Barringer Medal from the Meteoritical Society in 1985 and the Penrose Medal from the Geological Society of America in 1988.
Dietz was an outspoken critic of creationism, and was the faculty advisor of two student groups at Arizona State University in 1985, Americans Promoting Evolution Science (APES) and the Phoenix Skeptics. Dietz spoke on evolution and creationism at meetings of these groups, and debated creationist Walter Brown and Christian apologist William Lane Craig at Arizona State University.
The ASU School of Earth and Space Exploration sponsors annual Robert S. Dietz Memorial Public Lectures, which have been given by: