 The extremely hot, relatively buoyant plutons, also called "plutonic diapirs", intruded through denser, native country rock and sediments, never reaching the surface.At the same time, some magma managed to reach the surface as volcanic lava flows, but most of it cooled and hardened below the surface and remained buried for millions of years.The batholith – the combined mass of subsurface plutons – became exposed as tectonic forces initiated the formation of the Basin and Range geologic province, including the Sierra Nevada.