Tests of the discocyclinid foraminifer Pseudophragmina clarki occur in several 50-cm thick beds that are widely dispersed within alternating laminated and bioturbated sandstone of the Llajas Formation. At the 575-m thick type section, this sandstone makes up the interval from 100 to 370 m above the base of the formation.

Most of the beds consist of laminated to bioturbated, calcareous, very fine to fine quartzarenite; many are channel deposits, within which tests are concentrated in small pods. Turritella andersoni lawsoni may or may not occur with the discocyclinids, but if present it is the only megafossil. Associated foraminifers, listed in decreasing abundance, include Robulus, Nodosaria, Cibicides, Operculina, Asterigerina, and Quinqueloculina. Most of the genera are extant and are found today in tropical to subtropical shallow marine waters.

The fragile tests of Pseudophragmina clarki are mostly complete, unabraded, and 1.5 to 7 mm in diameter. Associated fossils also show no obvious signs of abrasion but they must have been transported because they occur in what are interpreted to be channels. Absence of significant abrasion and fragmentation is suggestive of minimal transport. P. clarki and associated fossils, therefore, constitute transported assemblages which are in the same environment in which they lived. The paleontologic evidence of a shallow marine environment is in keeping with the presence of the fossil beds within alternating laminated and bioturbated sequences. Modern examples of such sequences are found predominantly in inner shelf environments.

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