Detrital zircon grains for this study were sampled from Middle Triassic (Anisian) fluvial sandstone forming the Holbrook Member of uppermost Moenkopi Formation as exposed on a prominent butte near Winslow, Arizona. U-Pb ages of 100 detrital zircon grains were analyzed by LA-ICP-MS using a beam diameter of 50 microns. Analytical data were then filtered to reject grains with >20% age discordance, leaving 88 grains that yielded reliable results. Varied detrital zircon age populations include prominent clusters of Permian-Triassic grains (16% in the range of 240-270 Ma) and Neoproterozoic grains (7% in the range of 560-620), with the largest tight cluster being Mesoproterozoic grains (25% in the range of 1400-1500 Ma). Subordinate and more subdued age clusters include both younger and older Mesoproterozoic grains (16% Grenville in the range of 1000-1300 Ma; 16% Yavapai-Mazatzal in the range of 1600-1800 Ma). The Permian-Triassic grains were probably derived from the East Mexico arc, Paleozoic and Neoproterozoic grains most likely from the Ouachita-Appalachian orogen, and the sharp Mesoproterozoic cluster (1400-1500 Ma) almost certainly from granitic rocks intruded into the nearby Yavapai-Mazatzal belt of southwestern Laurentia. Other Mesoproterozoic grains could also have been derived from southwestern Laurentia, although Grenville grains could have come from the Ouachita-Appalachian orogen or nearby eastern Mexico (Oaxaquia). In nonmarine Moenkopi strata, paleocurrents flowing to the west and northwest toward marine equivalents in Utah and Nevada are compatible with a fluvial system with headwaters embracing southwest Laurentia (Yavapai-Mazatzal belt), the Marathon suture of the Ouachita system, and the Permian-Triassic East Mexico arc built on Gondwanan crust in eastern Mexico