Tbb
l
T
Basalt of Bimodal Suite (Pliocene and Miocene)
Dense black resistant alkali basalt in lava-flow layers 5-200 ft thick and interbedded tuffs and volcanic conglomerates.
Greatest preserved thicknesses are 900ft on White River Plateau and 800ft on Grand Mesa. Ages determined from several localities range from 8 to 23 m.y.
volcanic
mafic
basalt
feeder dikes
Tbbi
Basalt Dikes and Plugs (Pliocene and Miocene)
Probable feeders of basalt flows of Tbb unit; also intrusive into the flows; dike
dikes
Tb
gj
mr
Thb
d
Hinsdale Frm (Pliocene and Miocene; 4.7-23.4 m.y.) Basalt flows
Basalt flows-fine-grained alkali olivine basalt and basaltic andesite generally containing olivine phenocrysts. Xenocrysts of q
rhyolite
flows and necks
Thd