Insect fossil assemblages were analyzed from the Indian Peaks Wilderness and Rocky Mountain National Park. Assemblages span the last 10,000 years revealing climate change and the response of both insects and vegetation in the montane to upper subalpine zones. The Longs Peak Inn Bog site (LPIB) yielded insect assemblages ranging in age from recent to 3500 yr BP. This insect fossil record suggests climatic cooling at about 1800 yr BP and between 250 and 300 yr BP (AD 1700-1850). The bog may experience colder microclimates than the surrounding forests, yielding insect assemblages reflective of the colder, local microclimate. Also, alpine and upper subalpine insects may have been washed into the catchment basin of the bog from nearby slopes. Assemblages from four additional Front Range sites suggested a climatic optimum between 9000 and 7000 BP. Faunal evidence indicates a tree-limit decline at 4500 BP. Declining forest-tundra insect ratios, combined with the conifer macrofossil record, suggest a climatic deterioration from 4500 to 3100 BP followed by a rapid amelioration, from 3000 to 2000 BP. A gradual decline in the forest-tundra ratios occurred after 2000 BP, reaching 1:1 ratios at or before 1000 BP.