Paleo Slide Set: Packrat Middens: Vegetation & Climate Variability in the Southwestern United States
Vegetation Changes in the Grand Canyon

Packrat middens also allow the reconstruction of past vegetation at specific sites. The modern vegetation 
of Horseshoe Mesa within the Grand Canyon (top photo) is contrasted with a reconstructed image of what it 
may have looked like about 20,000 years ago at the height of the late Wisconsinan glacial period (bottom image).
A desert scrub of mormon tea, blackbrush, and cactus grows at this 5000' elevation site today. A few junipers grow 
along the cliff tops. The fossil vegetation was inferred from plant macrofossils from packrat middens collected 
within the caves in the Redwall Limestone along the center of each picture. Within the reconstructed ice age scene, 
the bottom slopes support a woodland of juniper, sagebrush, and shadscale, with Douglas fir and white fir growing 
in the shady cliff alcoves. A few limber pines grow along the cliff tops (Cole, 1982; 1985; 1990). Occasional 
collapses along the cliff face caused the landscape to migrate backwards at a rate of about 1.5 feet every thousand 
years, slightly altering the appearance of the cliff between images. 

Photo Credits:
Photo and computer reconstruction by Cole and Myer, 1982 
U. S. Geological Survey