The eastern end of the Matilija Sandstone and its inferred equivalents across the Santa Ynez and Pine Mountain faults were studied. These bodies of arkose have similar average modal compositions of quartz (31%), K-feldspar (21%) and plagioclase (22%). Accessory minerals also suggest derivation from a granitic basement complex. A few grains of serpentine and chert may reflect a minor contribution from a Franciscan terrane.

Depositing currents flowed mainly northwest, especially in the center of the basin. Influx of sand was probably from southern and (or) southeastern quadrants on the south side of the basin and from the northeast on the north side of the basin.

Local sand bars may have caused brackish-water environments on the southern and northern sides of the basin. The evidence is particularly strong in the area north of Pine Mountain. Coarse-grained, conglomeratic arkose with giant cross-stratifications are interbedded with strata containing shallow offshore mollusks and probable brackish-water mollusks.

Grain size and bedding thickness generally vary in direct proportion to each other. Thicker beds are usually in the thicker sections. Maximum areas of sand deposition appear to have swung back and forth producing overlapping lenticular lobes pointing into and down the basin.

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