We used leaf characters to estimate the paleoclimate of a Late Cretaceous floodplain depositional environment located in present-day northwestern New Mexico. Woody dicot species were collected from this area to determine the Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) using both uni- and multi-variate methods. From the same stratigraphic level within the Fruitland-Kirtland Formations, greater than 150 specimens from 3 sites representing more than 21 morphotypes were sampled. Specimens were plotted on a collection curve to ensure species numbers reached saturation during sampling. Leaf margin analysis, a technique that compares the percentage of entire margin to non-entire margin leaves, was used to measure paleo MAT. In addition, the relationship between the mean natural logarithm of the leaf areas of the species in a sample (MlnA) and precipitation was used to measure the paleo MAP. Our initial results indicate that the San Juan Basin was warm and humid during this time with a MAT of 26.2 ± 2.5°C and MAP of 118.1 cm. For another estimate of paleoclimate, a multivariate approach employing the CLAMP 3B database was used. Our initial results with this method indicate a MAT of 17.5°C with cold month mean temperature of 9.7°C and warm month mean temperature of 26.1°C and a mean growing season precipitation of 139.0 cm. These estimates are consistent with qualitative evidence, such as the presence of palms, gingers, weakly developed to absent growth rings in wood, and crocodilian remains. Differences between the temperature estimates may be due to several factors, such as taphonomic effects and sample size, and will be addressed. This research contributes to our knowledge of paleoclimate during the Late Cretaceous and provides measured variables to consider when comparing paleoecological data among regions.

Key words: Cretaceous, leaf physiognomy, paleoclimate