Valle Grande caldera makes up the center of the Jemez Mountains west of Los Alamos and is a late Neogene volcanic mass with the central crater sixteen miles in diameter—one of the world’s largest calderas. Bandelier National Monument headquarters is within a canyon carved from Valle Grande’s ashes. Volcanic ash scattered over the western parts of Texas, Oklahoma, and Kansas was blown from this volcano. Capulin Mountain, east of Raton, is a huge recent cinder cone and is surrounded by numerous basaltic lava flows that cap the High Plains from Raton eastward to Clayton. The very fresh black basalt flows near Carrizozo and in the valley of Rio San Jose near Grants are probably less than 1000 years old. Numerous mesas along the Rio Grande Valley from the Colorado line to El Paso are capped by black basalt flows of late Neogene age. Many of the present-day mountains were uplifted in early Neogene time, following the climax of the great volcanic eruptions. This uplifting, in many instances, took place along one side of huge mountain masses, forming tilted fault blocks like the Sandia, Manzano, San Andres, and Sacramento mountains. Rock beds in the Sandia Mountains, for example, dip to the east, but were uplifted along a west-bounding fault zone—a huge break in the earth’s crust—as much as four miles! This was an earth-shaking event! However, the uplifting took place slowly, and indeed is continuing today as the Albuquerque area, along with the Rio Grande Valley southward to Socorro, is one of the most active earthquake areas in the state. Concurrent with uplift, other blocks of the earth’s crust sank, forming graben basins which were flooded with rock debris from the adjoining uplifts. A tremendous irregular graben, now followed by the Rio Grande, cut north-south across the state. Geologists label it the _Rio Grande structural depression_ (fig. 3). Mountains on the east are the Sangre de Cristo, Sandia, Manzano, Los Pinos, Fra Cristobal, and Caballo ranges; those to the west include the Brazos, Jemez, Ladron, Socorro, Magdalena, and San Mateo mountains. Within this complex graben, and around the bordering ranges, the colorful sandstones and siltstones of the Santa Fe Group were deposited—these red, yellow, orange, and cream rocks are eroded in many places, such as near Santa Fe, to “badlands” characteristic of the landscapes along the Rio Grande Valley from Espanola southward to El Paso. Much brightly tinted silicified wood is found in these beds, and literally freight-car loads of mammalian remains have been shipped to museums from outcrops near Espanola.