Lava Beds National Monument Stronghold, which is 450,000 years old. Petroglyph Point was created about 275,000 years ago when cinders erupted through the shallow water of Tule Lake; violent explosions of ash and steam formed layers upon layers of tuff. The caldera is thought to have formed by subsidence, during which basalt and andesite were erupted up on the slopes. Lava flows dated to about 30,000–40,000 years ago formed most of the lava tube caves in the monument. As the hot basaltic lava flowed downhill, the top cooled and crusted over, insulating the rest of the lava and forming lava tubes. Lavacicles on the
Trap rock the Green with trap rock quarried from Eli Whitney's quarry, is a particularly colorful example of a red-orange-brown-colored, natural-faced trap rock. It was also used for foundations and railroad beds in the New Haven area. Well-known examples of outcropping trap rock include both intrusive sills and extrusive lava flows. They include the Palisades Sill, a Triassic, 200 Ma diabase intrusion that forms the Palisade along of the Hudson River in New York and New Jersey. Vast areas of trap rock in the form of thick lava flows and other volcanic rocks comprise the Deccan Traps of India and Siberian Traps