The Manzano Mountains, on the east edge of the Rio Grande Valley, are between Albuquerque and Abo Canyon, 40 mi south. Paleozoic rocks exposed in the range are chiefly of Pennsylvanian age. Rocks of Permian age crop out on the east flank of the mountains at the south end of the range.

Pennsylvanian and lower Permian rocks have been subdivided into three major lithic types--one constituting the Sandia Formation and two constituting the Madera Limestone. The Sandia Formation contains a basal sandstone and conglomerate, and upper beds of sandstone and dark-colored shale with a few thin beds of fusulinid-bearing limestone. The Madera Limestone overlies the Sandia Formation with apparent conformity. The lower part of the Madera is dominantly limestone (commonly cliff-forming) and a few thin beds of shale and minor amounts of sandstone. The upper part, which overlies the lower part with no more than minor disconformity, consists of rhythmically alternating sandstone and conglomerate, shale, and marine limestone. This upper part has been subdivided for convenience into un ts B, C, and D.

Fusulinids from the Sandia Formation indicate that these rocks were deposited during Atoka time. Fusulinids from the lower part of the Madera Limestone indicate deposition during Des Moines time. The upper part of the Madera is within the faunal zone of Triticites. The fusulinid fauna from unit B suggests deposition during Missouri time; that from unit C suggests deposition during early Virgil time; and that from unit D suggests deposition during late Virgil and early Wolfcamp times.

Studies of insoluble residues from 52 samples of fusulinid-bearing limestones from 5 measured sections suggest that there is correlation between the amount of terrigenous material in the limestone and the relative abundance of the fusulinids. If the amount of terrigenous material is taken to be an index of water turbidity, tentative conclusions may be drawn concerning clarity of the water in which the fusulinids lived.

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