Significant oil finds recently have been made in the northeasternmost Los Angeles basin. Exploration in the area has lagged because of supposed structural complexity and limited stratigraphic concepts. The development of stratigraphic concepts since the early 1950s now allows us to reinterpret and refine depositional patterns and resolve some of the structural complexity. Unlike other parts of the Los Angeles basin, land is still available in many areas and lease costs are reasonable, hence, a review of older records and recomputation of older geophysical work in addition to application of new and improved field and stratigraphic theory can lead to new oil finds. This is especially true along the basin edge with emphasis on source and distribution of sands. Exploration is best done before urbanization and attendant increased costs of operation.

The new West Mahala pool can be used as a case history. The pool was discovered by M. J. Castro as a stratigraphic trap in late Miocene, Puente Formation sediments. The producing measures are in fan and canyon turbidite deposits in upper to middle bathyal sediments (800-3,000-ft water depth). There are two producing zones--the Willis and Langstaff zones. The sandstone geometries suggest fan deposition for the Willis, and channel or canyon facies for the Langstaff. Recovery factors, gas drive, and decline rates are typical of sands given this interpretation. Porosity and permeability data support these contentions. Reworked and shallow-water foraminifers are considerably

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more abundant in the displaced shallow-water sands. The probability of finding other fields which are somewhat analogous to the West Mahala pool are good. Geologic models used in exploration should include deep-water turbidite fan-channel complexes which may be distributed along the northeast side of the Chino, Puente, and San Jose Hills.

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