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
Chinchillas (lava dome) Chinchillas (lava dome) Chinchillas is a lava dome complex in the northern Puna of the Andes, in the Sierra de Rinconada. The complex is constructed on an Ordovician basement called the Acoite Formation. In addition to the dacitic lava dome on the southern end of the complex it also contains small volume massive pyroclastic flows and ash-and-block flows. The complex has a volume of . The complex was formed 13±1 mya over a fault zone. Hydrothermal Ag-Pb-Zn deposits found there in breccia were mined occasionally. According to Coira "et al." (1996) it, Cerro Redondo and Pan de Azúcar may be