San Nicolas Island, off the coast of southern California, is the emergent part of a north-trending anticlinal ridge formed of middle Eocene sandstone, siltstone, shale, and conglomerate. The sedimentary units contain varied sedimentary structures, such as cross-bedding, oriented cobbles, and contorted lamination axes, which show that sediment-transporting paleocurrents were toward the southwest (vector mean of 193°).

Other sedimentary structures such as flat diffuse laminations, dish structures, outsized siltstone clasts, together with the lack of well-developed graded bedding suggest that the sediment was emplaced by mass-flow or grain-flow deposition. The presence of a bathyal microfauna, the association of lenticular units with laterally contiguous units, the high percentage of sandstone in the section, channels with imbricated conglomerates, and pebbly mudstone indicate that the section was deposited on the middle or suprafan part of a submarine fan or cone.