A scientific drilling effort has been proposed to deepen an existing 2-km deep hole to a target depth of between 3.5 and 4.0 km. The borehole is located near the center of the resurgent dome of Long Valley Caldera in east-central California. Deepening the well has been accomplished by continuous H-size coring (2.5" diameter core) to the target depth. Long Valley Caldera has shown sustained unrest since 1980 characterized by recurring earthquake swarms, inflation (dome-shaped uplift) of the resurgent dome, and increased levels of fumarolic activity accompanied by high concentrations of carbon dioxide (CO₂) gas in the soils around Mammoth Mountain on the southwest margin of the caldera.

Keywords: North America, USA, California, Long Valley, Caldera, Thermal Regimes, Volcanic Systems,