Beacon Rock is the core of an ancient volcano.
The ice-age floods through the Columbia River Gorge eroded the softer material away, leaving this unique geological structure standing by itself on the banks of the Columbia River. An attempt by Rick Conrey to obtain an age from Beacon Rock failed when no radiogenic gas was obtained, probably owing to relatively young age of the unit and high concentration of atmospheric argon in the sample. Uplift along the axis of the Columbia River gorge began well before Beacon Rock time. The amount of uplift since that time, on the order of 500 meters, can be reckoned by considering that the Portland reach of the river was within or nearly in tidewater influence, owing to the proximity of the marine strandline at the present Oregon coast. Increased understanding of Beacon Rock lava and its age may better constrain the uplift history by virtue of a bracketing youngest age and may provide additional insight into the history of downcutting by the Columbia River.