Rock Island Dam Island Pool. Rock Island Dam is constructed on Columbia River basalt similar to that which is exposed on the cliffs near the dam. These columnar basalts were formed from lava flows during the mid- to late-Miocene Epoch, some 14 to 16 million years ago. The rock is strong and durable and provides a very stable foundation for the structure. Columbia River stream flows at the Project averaged 73,700 cubic feet per second (2090 m³/s), a decrease of 37% from 2000 and 63% of the 20 year average of 116,700 cubic feet per second (3305 m³/s). The Rock Island Hydro Project
Cinder Cone and the Fantastic Lava Beds and the two Fantastic Lava Beds flows. The second Fantastic Lava Beds flow that all scientists but Diller thought had been erupted in 1851. At the Old Bench and Painted Dunes lava flows, the volcanic ash is brightly oxidized because it interacted with the lava flows when they were still hot. It shares its compositional group with the Fantastic Lava Beds flows, which represent the last flows erupted at Cinder Cone. Ultimately, the eruptive sequence at Cinder Cone took place over the course of several months. An unusual characteristic of the Fantastic Lava Beds is the presence of anomalous quartz