Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States
Laboratory preparation of midden sample.

The fieldwork associated with packrat midden analysis is very rewarding. Scientists conduct their 
research on cliffs and outcroppings with spectacular views, identifying the floral composition and 
relative age of the middens on the spot; the laboratory is where the tedious work begins. The midden 
sample, often as hard as a rock, is carefully cleaned with hammer and chisel, then immersed in water 
for one to two weeks to dissolve the crystallized urine and release the plant and animal remains. These 
remains are then dried in an oven. Each midden sample may contain tens of thousands of plant parts, which 
are sorted by species and either enumerated or weighed. The sorted materials are archived and then mined 
for special studies, which include the extraction and sequencing of ancient DNA. 

Photo Credits:
Kenneth L. Cole 
U. S. Geological Survey