Although Xenoxylon is a global genus of Mesozoic wood in the Northern Hemisphere, it is striking that the valid records in North America occur only in the northernmost parts of the continent. Decades ago, two species of Xenoxylon were described from the Upper Jurassic Morrison Formation in Utah, USA. However, a recent review of all North American reports of Xenoxylon excluded both species from the genus based on their anatomy, rendering all records of this genus south of Montana invalid in 2019. Here we describe a fossil log from the Morrison Formation near Vernal, northeastern Utah, USA, with true Xenoxylon anatomy with locally xenoxylean radial tracheid pitting and fenestriform crossfield pitting. Due to a novel combination of radial tracheid pitting, crossfield pitting and ray height, a newspecies, Xenoxylon utahense Xie et Gee sp. nov., is recognized here. Located at the southernmost occurrence of Xenoxylon in North America during the Mesozoic, this new species confirms that Xenoxylon trees were not only restricted to a circumpolar zone, but also grew in more southerly areas. In comparison with other fossil plants in the Morrison Formation of Utah, along with growth ring characteristics and climatic preferences of living conifers, the new fossil log with true growth rings with abundant, well-formed earlywood and extremely little latewood argues for a warm and humid climate with very mild seasonality for the Late Jurassic in this region, which is inconsistent with previous interpretations of Xenoxylon as a reliable indicator of cool climates. (C) 2021 Elsevier B.V. All rights reserved.