The DOSECC well in Cajon Pass encounters two sedimentary units: the uppermost is Unit 5 of the Cajon (Punchbowl) Formation; the lower has not been identified. To help identify the lower unit, 325 fragments of fossil tooth and bone were separated from 600 kg of cuttings recovered from 430-435 m in the well by washing, sizing, heavy liquid separation and hand sorting. The most diagnostic fossil is a rodent upper incisor with distinctive pinnate ridges. Such ridges are characteristic of those on upper incisors of Hemingfordian land mammal age squirrels of the tribe Sciurini. This date is consistent with local structural interpretations.
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