In 1973, Armstrong moved to Vancouver, British Columbia, Canada to be an associate professor at the University of British Columbia. He was eventually made a full professor. In 1979, he became a Canadian citizen. Armstrong studied the chronology of magmatism, metamorphism, and tectonics of western North America. He utilized several methodologies, including Potassium-Argon, Rubidium-Strontium, Uranium-Lead and Neodymium-Samarium to obtain isotopic data. Armstrong's early theories guided research for a generation. His views were controversial and contested by many prominent isotope geochemists. It took decades for other scientists to accept his ideas. Before he died, Armstrong was vindicated through the recognition he received for his model of crustal recycling at the 1990 ICOG meeting in Canberra after presenting a paper on "The Persistent Myth of Crustal Growth". Most of Armstrong's effort was spent systematically building an enormous database on the geochronology of the North American Cordillera. This database highlighted the magmatic evolution of the region and continues to provide a wealth of information to the scientific community. Armstrong was an active member of the Geological Society of America and editorial boards for several journals. He participated in the peer review process of the National Science Foundation and Canada's Natural Sciences and Engineering Research Council. He also participated in Canada's Lithoprobe program a national geoscience research project and contributed to the development of the geological timescale, particularly the Triassic. On August 9th 1991, Armstrong died of liver cancer, five days after his 54th birthday.
The Richard Lee Armstrong Endowment Fund, an endowed scholarship, was established at the Department of Earth Sciences, University of British Columbia after his death
A new radiogenic isotope laboratory was dedicated to his memory by the University of British Columbia
Armstrong, R.L.. 1966. K-ar dating of plutonic and volcanic rocks in orogenic belts: Age determination by potassium argon: Heidelberg, Springer-Verlag, pp. 117-133.
Armstrong, R.L.. 1968. A model for Pb and Sr isotope evolution in a dynamic earth: Reviews of Geophysics, v. 6, pp. 175-199.
Armstrong, R.L.. 1972. Low-angle faults, hinterland of the Sevier orogenic belt, eastern Nevada and western Utah: Geological Society of America Bulletin, v. 83, pp. 1729-1754.
Armstrong, R.L., 1988. Mesozoic and Early Cenozoic Magmatism of the Canadian Cordillera. doi: 10.1130/SPE218-p55 GSA Special Papers 1988, v. 218, pp. 55-92
Armstrong, R.L, Parrish, R.. 1990. A geologic excursion across the Canadian Cordillera near 49°N : Geological Association of Canada Meeting, Vancouver, May, Field Trip Guidebook, 71 p.
Harland, W.B.; Armstrong, R.L.; Cox, A.V.; Craig, L.E.; Smith, A.G.; Smith, D.G., 1990. A Geologic Time Scale, 1989 edition. Cambridge University Press: Cambridge, pp. 1-263.
Armstrong, R.L., 1991. The Persistent Myth of Crustal Growth. Austral. J. Earth Sci., Vol: 38:613-63