A piece of weathered Columbia River Basalt, collected in Tiger Canyon (SE Washington) at the contact between the Grande Ronde and Wanapum basalt groups. Approximately 15 million years ago this was the paleosurface. The veicularithy of this piece supports that this was the flow top of a Grande Ronde flow, and existed as a surface long enought to be weathered before it was covered by the next Wanapum flow.