This closeup of a Middle Topanga Formation conglomerate layer shows a light-colored granodiorite boulder at the point of the hammer, dark-gray quartz diorite cobble in the lower right and a brown basalt cobble at the center-top part of the photo. These eroded rock fragments in the conglomerate prove that the granodiorite and quartz diorite were exposed and were being eroded when the Middle Topanga Formation was being deposited. The basalt cobble proves that even the Middle Topanga Formation lava flows were being eroded and reincorporated into the Middle Topanga sedimentary layers.
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