Two main mineral assemblages are present in the upper part of the Popo Agie beds of the Chugwater (Triassic) Formation near Lander, Wyoming. These are: 1) quartz, montmorillonite and analcime; and 2) quartz, illite (shredded muscovite) and feldspar. The upper zone is 45.3 ft thick and is characterized by the quartz-montmorillonite-analcime assemblage. Montmorillonite in association with analcime suggests that the analcime may have originated from volcanic material.

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