The kind of Late Pleistocene organic deposits that yield
abundant insect fossil remains are quite rare in the Rocky
Mountains, because many of the mountain ranges were glaciated during the Lastglaciation. The movements of glacial ice scoured
high-elevation landscapes, obliterating older organic-rich sedimentary
deposits. Therefore the high elevation fossil assemblages
discussed here either represent postglacial times (i.e., after the ice
margins retreated back upslope from the sites), or they were
formed in rare high elevation localities that remained ice-free,
such as the Ziegler Reservoir site near Snowmass, Colorado. A
brief description of the study sites follows, in north-to-south
order.