The group is composed primarily of
volcaniclastic beds, deposited in
alluvial fans or
braided streams, with minor
basaltic andesite to
dacite lava flows. The total thickness is as much as .
Formations The group is divided into numerous formations. In descending stratigraphic order, these are: • South Crosby Peak Formation • Rincon Windmill Formation • Chavez Canyon Formation • Dog Springs Formation •
Rubio Peak Formation •
Palm Park Formation • Pueblo Creek Formation •
Bell Top Formation • Rock Springs Formation In addition, a number of informal units have been described within the group. ==History of investigation==