ðə tˈɑːp ʌvðə dənˈɑːzˈɪn mˈɛmbɚ, wˌɪtʃ kəntˈeɪnz ðə wˈɪloʊ wˈɑːʃ lˈoʊkəl fˈɔːnə, hˈæzbiːn dˈeɪɾᵻd tə sˈɛvənti θɹˈiː.fˈoːɹɾi nˈaɪn plˈʌs ɔːɹ mˈaɪnəs zˈiəɹoʊ.twˈɛnti fˈaɪv mˈɑː ɐɡˈoʊ.
The top of the De-na-zin member, which contains the Willow Wash local fauna, has been dated to 73.49 ± 0.25 Ma ago.