The various fossil beds of the Green River Formation span a five million year period, between 53.5 and 48.5 million years ago (mya). During this period the climate moved from the moist early Eocene climate and the slightly drier mid-Eocene.
ð ə WORD_BOUNDARY v ɛ ɹ iə s WORD_BOUNDARY f ɑ s ə l WORD_BOUNDARY b ɛ d z WORD_BOUNDARY ʌ v ð ə WORD_BOUNDARY ɡ ɹ iː n WORD_BOUNDARY ɹ ɪ v ə ɹ WORD_BOUNDARY f ɔ ɹ m eɪ ʃ ə n WORD_BOUNDARY s p æ n WORD_BOUNDARY ʌ WORD_BOUNDARY f aɪ v WORD_BOUNDARY m ɪ l iə n WORD_BOUNDARY j ɪ ɹ WORD_BOUNDARY p iə ɹ ɪ ə d WORD_BOUNDARY b ɪ t w iː n WORD_BOUNDARY f ɪ f t i WORD_BOUNDARY θ ɹ iː WORD_BOUNDARY f aɪ v WORD_BOUNDARY æ n d WORD_BOUNDARY f ɔ ɹ t i WORD_BOUNDARY eɪ t WORD_BOUNDARY f aɪ v WORD_BOUNDARY m ɪ l iə n WORD_BOUNDARY j ɪ ɹ z WORD_BOUNDARY ʌ ɡ oʊ WORD_BOUNDARY ɛ m w aɪ eɪ WORD_BOUNDARY d ʊ ɹ ɹ ɪ ŋ WORD_BOUNDARY ð ɪ s WORD_BOUNDARY p iə ɹ ɪ ə d WORD_BOUNDARY ð ə WORD_BOUNDARY k l aɪ m ə t WORD_BOUNDARY m uː v d WORD_BOUNDARY f ɹ ʌ m ð ə WORD_BOUNDARY m ɔɪ s t WORD_BOUNDARY ɜː l i WORD_BOUNDARY iː ə s iː n WORD_BOUNDARY k l aɪ m ə t WORD_BOUNDARY æ n d WORD_BOUNDARY ð ə WORD_BOUNDARY s l aɪ t l i WORD_BOUNDARY d ɹ aɪ ə ɹ WORD_BOUNDARY m ɪ d iː ə s iː n WORD_BOUNDARY