The base of the Kirtland Formation and its lowest sub-unit, the Hunter Wash member, has been dated to 75.02 ± 0.13 Ma.
ðə bˈeɪs ʌvðə kˈɜːtlənd fɔːɹmˈeɪʃən ænd ɪts lˈoʊɪst sˈʌbjˈuːnɪt, ðə hˈʌntɚ wˈɑːʃ mˈɛmbɚ, hˈæzbiːn dˈeɪɾᵻd tə sˈɛvənti fˈaɪv.zˈiəɹoʊ tˈuː plˈʌs ɔːɹ mˈaɪnəs zˈiəɹoʊ.θˈɜːtiːn mˈɑː.