The structural evolution of the Wilmington anticline in the Los Angeles basin, California, began with middle Miocene folding which probably was not coincident with the present anticlinal axis. The ancestral fold was truncated prior to the start of late Miocene deposition. Uninterrupted sedimentation occurred throughout the late Miocene.

No evidence of the present Wilmington anticline is seen prior to the deposition of the lower part of the Ranger zone. The source of sediment supply was in the northeast and the direction of transport, southwest.

Growth of the Wilmington anticline was initiated in late Miocene, during deposition of the early Ranger zone. Most Ranger subzone isopachs reflect Ranger structure, and demonstrate continuous anticlinal growth during the early Repettian Stage of the Pliocene. Movement on the Long Beach Unit fault began during deposition of the Ranger X sand and culminated at the close of F sand deposition. The F sand was eroded and channeled by current action along and across the anticlinal axis prior to Fo sand deposition.

The Fo sand was deposited as a lens-shaped body on the eroded F, and is present over a minimum 48-sq-mi (124.3 sq km) area. No evidence of structural growth during the deposition of this sand is present, in contrast to the other Ranger sands. The Fo is thought to be primarily a tractionite.

Renewed uplift and additional movement on earlier faults occurred throughout the Repettian Stage. Uplift and truncation of the Repettian occurred prior to the deposition of the Pliocene Pico Formation.

Southward tilting during the middle Pleistocene Pasadenan orogeny completed the Wilmington structural evolution.

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