McPhee characterized him in Basin and Range (1981): "Deffeyes is a big man with a tenured waistline.
[4] Deffeyes Ph.D. dissertation research concerned volcanic ashfalls in Nevada that had been altered to zeolites.
Zeolites have important uses in water purification, as catalysts in the petrochemical industry, and as molecular sieves.
On February 11, 2006 Deffeyes claimed that world oil production had peaked on December 16, 2005.
[5] In John McPhee's 1981 book Basin and Range, about the origin of Basin and Range topography, Deffeyes teaches geology to McPhee and his readers by analyzing road cuts and the exposed geologic strata that resulted from the construction of Interstate highway 80.