SIERRA GRANDE SHIELD VOLCANO
The Raton-Clayton Volcanic Field is an elongated,WNW-ESE trending, ~140 km-long lava & volcano field in northeastern New Mexico and southern Colorado. It consists of cinder cones, spatter cones, shield volcanoes, and fissure vents. Erupted materials range from mafic to intermediate to alkaline lavas (basalts, basaltic andesites, andesites, dacites, nephelinites, basanites).
The largest volcano in the field is the Sierra Grande Shield Volcano. Shield volcanoes have a low, broad profile. The largest volcano on Earth is this type (Mauna Loa Volcano, Hawaii Hotspot), and the largest volcano in the Solar System is this type (Mt. Olympus Volcano, Olympus Hotspot, Tharsis region, Mars).
Sierra Grande Shield Volcano (looking SE from atop Capulin Cinder Cone) - this is the largest volcano in the Raton-Clayton Volcanic Field. It's located to the south and southwest of the small town of Des Moines in northwestern Union County, northeastern New Mexico, USA.
Sierra Grande Andesite (7.3 cm across at its widest) - vesicular andesite from lava flow on the eastern side of Sierra Grande Shield Volcano, Raton-Clayton Volcanic Field, northeastern New Mexico, USA (36° 42’ 24.26” North, 103° 47’ 46.75” West). This lava flow is from the upper Upper Pliocene, dating to 1.9 m.y. The rock consists of generally small phenocrysts of augite pyroxene, hypersthene pyroxene, olivine, and plagioclase in a glassy to microcrystalline groundmass dominated by feldspar, pyroxenes, plus some other minerals.