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When examining the over-all picture of the Ventura basin, one is impressed by the number of large thrust faults which occur. These east-west faults are among the most predominant structural features of the area. Much of the present topography is controlled by these faults. There is good evidence that much of the movement of these faults occurred during the Pleistocene and some of them may have been active as late as that period of chronological confusion when the Pleistocene ended and the Recent began. In several places a north-dipping fault overrides a south-dipping fault, indicating that there were probably two periods of faulting. The displacement of these faults varies from that of a few hundred feet to as much as 20,000 feet. If known rates of movement now occurring n Southern California are applied to these faults, it is possible to postulate that more than 600,000 years were required for the displacement to have taken place on some of the larger faults.
Many of the Ventura basin oil fields are closely associated with these thrust faults. The four predominant relationships are as follows.
1. Anticlinal accumulation on the upper plate. The Oak Ridge oil fields are examples.
2. Accumulation on the upper plate against the fault such as in the Ramona field.
3. Oil zones are repeated. This occurs in the Oak Canyon field.
4. Subfault accumulations such as in the Timber Canyon and Ojai fields.
In conclusion it is suggested that further exploration along these fault trends will discover more oil.
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