The range is composed of a diverse group of mostly igneous rocks dating from the Devonian to Early Triassic Periods.
Smithian, a regional geological stage of the Early Triassic epoch (249.7 – 247.4 Ma) preceded by the Dienerian and followed by the Spathian
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It is known from several skulls and some postcranial material found from the Argana Formation in Morocco, which dates back to the Early Triassic.
They were collected from the "Couches à Poissons et Ammonites" Member of the Middle Sakamena Formation at the only currently known amniote locality of the Diego Basin, Antsiranana of northwestern Madagascar, dating to the Induan stage of the early Early Triassic period.
The Kinnerton Sandstone Formation (named from the twin villages of Higher and Lower Kinnerton on the England/Wales border west of Chester) is a sequence which ranges from 0m to over 150m thickness of largely aeolian sandstones of early Triassic age.