"One of the most
versatile...geologists of his generation." 
Geomorphology: The study of the
surface configuration of the earth, especially the nature and
evolution of present landforms, their relationships to
underlying structures, and the history of geologic activity as
represented by such surface features.
Joseph Hoover Mackin always thought of himself as a geomorphologist. But, over time, he became an engineering geologist, working on dam and reservoir problems, a structural geologist and map maker, an economic geologist, successful in locating and characterizing ore deposits, a field petrologist expert in volcanic ash flows and flood basalts, and finally, one of the foremost lunar geologists of the Apollo era.
"The striking thing about Mackin is how he became an expert in so many different areas," says UW geology professor Eric Cheney. "So often, scientists struggle their entire careers to become expert in one very narrow specialty. But Mackin would enter a field and within a short time became an expert in it, then go on to a new field and make another breakthrough. And he did this time and time again."
Mackin was the first to realize that the gentle slopes (pediments) along the northern Rockies were mature erosion surfaces. The fashionable idea of the time held that ultimately, erosion processes always produced entirely flat surfaces (peneplains). He is credited with recognizing that mature erosion surfaces could remain gently sloping.
Soon after joining the UW faculty in 1934, Mackin became
involved in studying the engineering geology of dams and
reservoirs in the Cedar and Snoqualmie Valleys in the Cascade
Mountains. In the course of that work, Mackin and students
discovered "a surprising but incontestable fact": the alpine
glaciers high up in the Cascades never came in contact with the
huge ice sheets of the last ice age. The alpine glaciers were
actually in retreat at the time when the Puget Lowlands were
covered by continental ice flows.
Mackin joined the Strategic Minerals Program of the U.S. Geological Survey during World War II, where he evaluated the reserves of iron ore deposits at Iron Springs in southwest Utah. Mackin determined the origins of these ore deposits, including the role of hydrothermal leaching of iron-bearing minerals from surrounding rocks as the source of the iron in iron deposits; and he elucidated other structural and chemical factors that govern the formation of such deposits. "Years later, these became the standard concepts of mineral exploration for many types of ore deposits," bringing Mackin much recognition, notes UW geology professor Eric Cheney.
A memorial in the Proceedings of the Geological Society of America calls Mackin's 1948 paper on graded streams "one of the most influential studies in this complex and difficult field." And he is credited with solving the stratigraphy of the extensive Columbia River basalts of central Washington State.
