Robert Roy Coats (1910–1995) was an American geologist known for his studies of the Aleutian Islands and his exhaustive report of Elko County, Nevada. He was born in Toronto, Canada, and grew up in Marshalltown, Iowa and Seattle, Washington. He graduated valedictorian of his high school class in Seattle at the age of 16, and attended the University of Washington, where he received both a B.S. and M.S. degree in Geology and Mining (1931 and 1932). He continued graduate work at the University of California, Berkeley, receiving his doctorate in 1938, with a thesis on the ore bodies of the Virginia City mining district in Nevada. He was known as an eccentric and brilliant student. In 1937, Coats took a teaching job at the University of Alaska Fairbanks. He left that job for a post with the U.S. Geological Survey in 1939, in Washington, D.C. As part of the Alaska Branch of the USGS, he continued working in Alaska, mapping in the Chichagof, Anikovik, Nome, Solomon, Kigluaik and Kobuk River areas, among others. During World War II, he spent time in the Aleutian Islands, returning in 1946 as part of the Survey’s Volcano Project. His field work in the Aleutians led to his 1962 paper (see references) on the origin of the Aleutian island arc. That prescient synthesis of tectonics and magmatism of the Aleutian arc contained several of the essential ideas of the subsequent paradigm of plate tectonics. He correctly interpreted: that the origin of the dipping zone of seismicity beneath the Aleutian arc occurs along a megathrust above underthrusting oceanic crust and its sedimentary cover; the relation between the position of the active volcanoes and depth to the underthrust oceanic crust; the role of fluids derived from the down-going slab and magmatic differentiation in determining compositions of erupted volcanic rocks (See Figure 1). Coats’s colleagues from the Alaska Branch of the USGS have commented on his extraordinary ability to comprehend the detailed geologic history of an area with only the most cursory examination. Visiting the Aleutian islands of Buldir, Adak, Kanaga, Semisophochnoi, Gareloi, Kiska and Amchitka (among others), typically for 1–2 days in notoriously bad weather, he produced geologic reports of such detail, insight and quality that they remain today, even in the face of much additional work, the prime source for understanding Aleutian geology. From 1951 to 1954, Coats was engaged in the search for radioactive granitic