Cultural changes during this period, including the earliest evidence for cultivation of corn and cotton, occur concurrently with changes in available moisture.
The Colorado River basin is home to more than 40 dams and diversions and functions more as a system of regulated canals and reservoirs than a river.
Scientists and managers in the Sierra Nevada parks have long recognized the essential nature of fire in these forests and have responded over the years with an increasingly sophisticated fire restoration program using both prescribed burns and natural fires.
Fire management and restoration programs in the Sierra National Parks now reflect much of what researchers like van Wagtendonk and Stephenson have learned about the behavior and ecology of wildfires. The current prescribed burning program, says Stephenson, is highly successful.
Although humans have long shaped their landscapes through deliberate use of fire, Allen says fire patterns in the Southwest have largely been driven by the region’s weather patterns.
The damming of the Colorado River at Glen Canyon is high on the West’s “greatest ecological sins” list.
Tucked away in remote Tsegi Canyon, the monument surrounds a small desert oasis, a place abundant in plant life, with mountain mahogany, Gambel oak, serviceberry, rice grass and Douglas fir scattered across the canyon.