Course of the Colorado River Davis Dam in Pyramid Canyon above Laughlin, Nevada, where a bridge carries NV 163 (Laughlin Highway)/AZ 95 over the Colorado River. Prior to the completion of the Hoover Dam Bypass project in 2010, this bridge was the main crossing for freight traffic between Arizona and Nevada as trucks were not allowed over Hoover Dam for security reasons after the September 11, 2001 attacks. The Colorado then passes by Bullhead City, Arizona and Fort Mohave, Arizona and the Fort Mojave Reservation. The Colorado forms the border of California to the west and Arizona to the east for most of its course
Flora of the Arizona Upland Flora of the Arizona Upland Flora of the Arizona Upland' includes higher elevation Sonora Desert plants that require more moisture and cooler climates than those of the adjacent Sonoran Desert areas in the Colorado Desert of the lower Colorado River valley area, and which can withstand frost, unlike plants of the Sonoran Desert south of the border between the United States and Mexico. The Arizona Upland receives between 12 and 15 inches of annual precipitation, of which half falls in the summer monsoons. Cold air collects in the valleys. Less cold tolerant species grow on the warmer slopes above. The