Paleoclimate and paleoelevation of the Oligocene Pitch-Pinnacle flora, Sawatch range, Colorado

Angiosperm leaves from the Oligocene Pitch-Pinnacle flora, which grew between 32.9 and 29 Ma, are described for the first time. This flora is especially interesting because it grew in a tectonically active region around the time of the precipitous Oligocene temperature drop and thus provides important constraints on paleoclimate and paleoelevation. New multiple regression models are developed from the modern vegetation leaf physiognomy data set of J. A. Wolfe and, when applied to the Pitch-Pinnacle flora, suggest a mean annual temperature (MAT) of 12.7 +/- 1.5 degrees C, with cold month and warm month means of 4.5 +/- 2.2 degrees C and 20.4 +/- 2.5 degrees C, respectively, and a mean annual range of temperature of 18.5 +/- 3.8 degrees C. Growing season precipitation is estimated to have been 101 +/- 16 cm, with this rain falling mostly during the nongrowing season, When the MAT estimate for the Pitch-Pinnacle flora is combined with MAT estimates for coeval floras from the coast, the implied elevation is either 2-3 km if the flora is pre-Oligocene deterioration, or around 1 km if post-deterioration. Paleodrainage reconstructions suggest the former, but more data are needed to resolve this issue.