Not more than 80 years ago the mighty Colorado River flowed unhindered
from northern Colorado through Utah, the Grand Canyon, Arizona, and
Mexico before pouring out into the Gulf of California. But as one can
see in this image of the Colorado River Delta taken on September 8,
2000, by the Spaceborne Thermal Emission and Reflection Radiometer
(ASTER), flying aboard the Terra spacecraft, irrigation and urban sprawl
now prevent the river from reaching its final destination.
The Colorado River can be seen in dark blue at the topmost central part
of this image. The river comes to an end just south of the multicolored
patchwork of farmlands in the northwestern corner of the image and then
fans out at the base of the Sierra de Juarez Mountains. A hundred years
ago the river would have cut through this entire picture and plowed
straight through to the Gulf of California, the mouth of which can be
seen in solid blue at the lower righthand corner of the image. Nearly
all the water that flows into the Colorado River is now siphoned off for
use in crop irrigation and for residential use. In fact, roughly only 10
percent of all the water that flows into the Colorado makes it into
Mexico and most of that is used by the Mexican people for farming.
The bluish purple river that appears to be flowing from the Gulf of
California to the north is actually an inlet that formed in the bed of
the Colorado River after it receded. The island at the entrance to the
Gulf of California is the Isle Montague. The gray areas surrounding this
inlet and the gulf itself are mud flats created by sediments once
carried by the river. The Hoover Dam built in 1935 and the Glen Canyon
dam built in 1956 now trap most of the river's sediments long before
they find their way to the gulf.
As to the other features on the image, the flat yellow expanse to the
east of the farms is the Gran Desirto. Between the farmland and the
desert one can see a dark blue pool covered with patches of green.
Known as Sienega de Santa Clara, this salt-water marsh formed by return
irrigation is home to a huge population of birds, including the
endangered Yuma Clapper Rail and the Southwestern Willow Flycatcher. The
white patches to the southeast of this swampy area are salt packs that
separate the marsh from the near lifeless salt lake extending east.
The Colorado River is the largest watershed in the southwestern US, emptying into the Salton Trough before reaching the Sea of Cortez. Over the past 2-3 million years, river sediments built a delta that extends from the US-Mexico border for a distance of 87 miles (140 kilometers). However, today the Colorado River delta is undergoing significant erosion and diminishing in size due to the lack of sediment replenishment from upstream sources.