title: Comment on "Apatite 4He/3He and (U-Th)/He evidence for an ancient Grand Canyon".
abstract: Flowers and Farley (Reports, 21 December 2012, p. 1616; published online 29 November 2012) use thermochronometry to propose that the western paleo-Grand Canyon was nearly as deep 70 million years ago (Ma) as today. However, lithologies, facies relations, geomorphology, and paleotopography of Miocene interior-basin deposits near the mouth of the Grand Canyon show that no paleocanyon existed in that area during filling of the basin, ~17 to ~5 Ma.
authors.affiliation: US Geological Survey, Flagstaff, AZ 86001, USA. ilucchitta@gmail.com
authors.forename: Ivo
authors.initials: I
authors.lastname: Lucchitta