A regional palaeoenvironmental reconstruction is presented for a north-south transect of late glacial pollen and insect fossil sites from the Rocky Mountain region. Altitudinal treelines were depressed by an average of 671 m. and summer temperatures were an average of 5. 4°C lower. The interpretation of palaeoenvironmental conditions based on insect fossil evidence tends to show stronger departure from modern parameters than that based on palynology. While clear evidence for late glacial occupation of the region by Palaeoindians is scarce, montane conditions were not so severe as to preclude human occupation, at least on a seasonal basis. Newly discovered sites of early occupation would benefit greatly from interdisciplinary studies.