Quercus hiholensis

Quercus hiholensis is an extinct species of oak in the Fagaceae genus Quercus. Quercus hiholensis is known from Middle Miocene fossils found in Central Washington.

The species was first described from specimens of silicified acorns preserved in chert of the "Yakima Canyon Flora". The chert was recovered from the "Hi hole" site, one of the "county line hole" fossil localities of the "Yakima Canyon Flora" located north of Interstate 82 in Yakima County, Washington. The "Hi hole" site works strata which was thought to be part of the Museum Flow Package within the interbeds of the Sentinel Bluffs Unit of the central Columbia Plateau N₂Grande Ronde Basalt, Columbia River Basalt Group. The Museum Flow Package interbeds, designated the type locality, are dated to the middle Miocene and are approximately 15.6 million years old. Later re-evaluation of the "hi hole" site indicated that the site is included into a basalt flow, rather than part of the interbedded Museum flow package. The evaluation suggested the basalt is part of the Wapanum Basalt and that the fossils are possibly a little younger then formerly reported. Dating reported in 2007 of a related site near Ellensburg, Washington, confirmed that the deposits worked are pockets within the basalt flows, and the 15.6 million year old date was accurate.

At the time of study, the holotype acorn, specimen UWBM 45-I, and a series of paratype specimens are preserved in the Burke Museum of Natural History and Culture, while additional examined fossils that were not part of the type series were part of the paleobotanical collections at Arizona State University. The specimens represent a range of preservation conditions, ranging from exposed on weathered surfaces of the chert, totally weathered out of the chert, and as hollow chert casts of the acorns. A total of 42 specimens in chert were studied by paleobotanists Sandra Borgardt and Kathleen Pigg, with their 1999 type description being published in the American Journal of Botany. Borgardt and Pigg chose the specific epithet hiholensis as a reference to the "Hi hole" locality that is the type locality of the species.