The middle Miocene Columbia River Basalt Group is the youngest and smallest continental flood basalt province on Earth, covering over 210,000 km² of mainly Oregon, Washington, and Idaho, with an estimated basalt volume of ~210,000 km³. A well-established regional stratigraphic framework built upon six formations contains numerous flows and groups of flows that can be readily distinguished by their physical and compositional characteristics, thus producing mappable units, the areal extent and volume of which can be calculated and correlated with their respective feeder dikes. The distinct physical features that help to define these units originated during their...