The Midland fault can be traced in the subsurface about 30 miles from the Bunker gas field southward through the Rio Vista field. This steeply dipping normal fault has a maximum vertical displacement of 3,000 feet, all movement occurring between late Paleocene and early Oligocene time. Up to 2,000 feet of Meganos, present on the downthrown western side, is absent on the eastern side, This earliest movement was contemporaneous with deposition or occurred during the post-Meganos pre-Capay regional uplift and tilting. Intermittent movement was contemporaneous with Capay and Domengine deposition, with greater thicknesses being deposited on the downthrown side. There has been a maximum of 600 feet of post-Domengine pre-"Markley" Gorge (Oligocene?) movement. Many gas accumulati ns of the area are modified or controlled by the Midland and adjacent smaller faults.

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