Geologic units in Los Alamos county, New Mexico

Bandelier Tuff (Lower Pleistocene) at surface, covers 69 % of this area

Includes large blocks of older andesite in caldera-collapse breccia facies locally exposed on resurgent dome of the Valles caldera.

Silicic to intermediate volcanic rocks (Neogene, mostly Miocene) at surface, covers 20 % of this area

Rhyolite and dacite flows with associated minor tuffs. Commonly interbedded with Santa Fe or Gila Group sedimentary units. Dacitic lavas in northern Jemez Mountains are Pliocene.

Upper Santa Fe Group (Middle Pleistocene to uppermost Miocene) at surface, covers 5 % of this area

Includes Camp Rice, Fort Hancock, Palomas, Sierra Ladrones, Arroyo Ojito, Ancha, Puye, and Alamosa Formations.

Basaltic to andesitic lava flows (Pliocene) at surface, covers 4 % of this area

Includes minor vent deposits and small shield volcanoes. Flows are commonly interbedded in the Santa Fe and Gila Groups.

Landslide deposits and colluvium (Holocene to Pleistocene) at surface, covers 2 % of this area

Landslide deposits on western flanks of Socorro Mountains not shown for clarity.

Intermediate to silicic volcanic rocks (Neogene) at surface, covers 0.3 % of this area

Mostly andesitic to dacitic strato volcanoes. Includes rhyolite lavas and tuffs in the Jemez Mountains, Volcanoes in Jemez Mountains and eastern Colfax County are upper Miocene. Mount Taylor and composite volcanoes in the Taos Plateau volcanic field are Pliocene.

Older rhyolite lavas and early volcaniclastic sedimentary fill deposits of the Valles caldera (Lower Pleistocene) at surface, covers 0.3 % of this area

Units are associated with resurgent doming or predate doming of the caldera core. Includes minor middle Pleistocene tuffs of the upper Valles Rhyolite on north side of caldera.

Piedmont alluvial deposits (Holocene to lower Pleistocene) at surface, covers < 0.1 % of this area

Includes deposits of higher gradient tributaries bordering major stream valleys, alluvial veneers of the piedmont slope, and alluvial fans. May locally include uppermost Pliocene deposits.