Regionally extensive mafic rock formations, or flood basalts, are a distinguishing feature of the geology of the Pacific Northwest and the Big Sky Carbon Sequestration Partnership. The region’s Columbia River Basalt Group (CRBG) covers approximately 164,000 km2 and is probably the most well studied igneous province in the world. The Snake River Plain basalts stretching across Idaho and High Lava Plains of Oregon add to the potential storage resource area. There are over 300 lava flows that comprise CRBG alone and each flow is from a few tens of meters to 100 meters thick. All combined, the BSCSP basalt formations offer significant longterm storage potential, with conservative estimates of CO2 storage capacity in the range of 50 - 100 billion metric tons. Basaltic provinces, however, are not limited to the Pacific Northwest. They are found throughout North America and may provide local carbon storage sites for areas lacking more traditional storage opportunities in saline formations or oil and gas fields. In the Big Sky Region, the Columbia River Basalt formations were formed millions of years ago as lava flows cooled on the earth’s surface. As successive flows cooled over time, layers of basalt were formed, each tens to hundreds of feet thick. The exterior portions of each layer cooled quickly forming cracks and bubbles, while the slow-cooling interiors cooled slowly creating dense and impermeable layers. The dense interior sections serve as cap rocks while the porous exterior sections serve as potential injection zones for CO2 storage. Laboratory tests have shown that basalts are very geochemically reactive and have the ability to chemically trap CO2 in a short period of time by forming solid minerals. When basalts have been exposed to supercritical CO2 and water in the lab setting, minerals in the basalt react with the CO2 and water to form limestone or calcium carbonate. This geochemical process traps the CO2 in a solid form and permanently isolates it from the atmosphere. Similar mineralization processes happen in other rock types but at much slower rates.