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IGNEOUS - EXTRUSIVE: Basalt cliffs, Grand Mesa --- Tertiary basalt flowed down a valley and hardened. Later erosion formed these cliffs where the hard basalt caps the mesa. Grand Mesa is an inverted valley -- what was low has now become high.
Basaltic rubble at the front of a lava flow with the stratovolcanoes of the Nevados de Chillan, Chile, in the background.
Elongate vesicles in basalt from the Bonito Lava Flow, west of Sunset Crater, AZ. Gas bubbles trapped in the lava originated these cavities, with the stretching related to a preferential direction of flow. This example of volcanic activity is about 1,000 years old, and is part of a larger Volcanic Field (San Francisco Volcanic Zone, AZ, USA).