These form a group of low cones or shield volcanoes and range in age from 27 to 23 million years old.

Younger basalt flows and silica-rich dacites and rhyolites are excluded from the current definition of the unit.

[1] The formation overlies the Bloodgood Canyon Tuff[2] or eolian sandstones[3] and is in turn overlain by the Gila Conglomerate.

[2] It is found throughout the Mogollon-Datil volcanic field as far southeast as the Black Range,[4] and is included in the upper Mogollon Group.

[6] The unit is locally separated into lower and upper informal members by interbedded tuffs, such as the rhyolite of Angel Roost.