The study of Quaternary insect fossils has shown their value as palaeoenvironmental indicators, especially during times of rapid climatic change, and this method is now being introduced into North American archaeological studies. Abundant insect fossils have been recovered from 13,000 year old detrital organic materials from silty clays at the Lamb Spring site, south of Denver, Colorado. The spring deposits also contain bones of extinct camel and mammoth, thought to have been modified by human hunters. The late Pleistocene insect fauna from Lamb Springs comprises 71 identified taxa from 6 orders and 14 families, principally beetles, providing substantial palaeoenvironmental data. The beetle fauna is a mixture of grassland and mountain elements, and they appear to represent an environment similar to that found today in high mountain valleys, such as South Park, Colorado. Based on this fauna, mean summer temperatures at 13, 140 BP were probably 10°C cooler than present.