Coordinated research on vitrinite reflectance, rock temperature, first occurrence of laumontite, and burial history at five sites in the Los Angeles basin and one in the Ventura basin resulted in significant findings regarding late Miocene and younger rocks. Data from 17 boreholes (reaching as deep as 5,800 m), including 110

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samples of conventional core, were studied. We believe that the present temperatures are maximal in the history of these late Miocene and younger rocks. The determined gradients are 24 to 35°C/km and 0.033 to 0.090% vitrinite reflectance per kilometer.

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