The metamorphosed Fairview Valley Formation (Permian-Triassic?) crops out beneath the Sidewinder Volcanics in the Mojave block, southern California. Abundant spherical grains occurring in its upper portions are questionably known as ooliths. However, results of field and mineralogical analyses lead to the conclusion that the majority of the grains are not ooliths but pisoliths originally formed in a sandy vadose zone. Their accretionary growth process began around siliceous nuclei in a similar manner to that of pisolith growth in caliche soil. Most of them commonly occur fused together or form unusual fitted polygonal structure.

Locally, the grains crop out as conspicuous graded, inverse graded, and lensoid or wavy beds. These are commonly separated by thin laminae composed of finely crystalline aggregates originally deposited as carbonate mud. This bedding suggests periodic accumulation under uniform, quiet-water conditions. No cross-beds or fossils were found in these deposits.

The average grain size of 466 pisoliths measured in the field ranges from 0.2 to 0.5 cm in diameter. The average size decreases vertically toward the upper (north) stratigraphic zones, which implies that either the pisoliths in the source area became smaller in size with time or they were brought from farther away. The bulk of the pisoliths is interpreted as having been carried a short distance from the source area by running water, and redeposited from waning currents similar to turbidity flows. The site of deposition was probably a nearby broad barred lagoon in proximity to a shallow marine environment, which would allow dolomitization to take place after burial of sediments.

The matrix of rock samples analyzed both by X-ray diffraction and staining contains iron-free calcite, tremolite, and forsterite. Prior to metamorphism, the matrix was possibly composed primarily of dolomite; presently, the pisoliths are formed mainly by diopside, iron-free calcite, wollastonite, dolomite, forsterite, and periclase. The calcite content in most pisoliths, especially the larger ones, seems to increase outward from the core.

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