Geoscience Reference
In-Depth Information
h e Great Basin valley l oors contain huge expanses of salty sediments
that are the remains of vast ice age lakes. h e Great Salt Lake desert, covering
some 20,000 square miles of western Utah, is one such region. It was made
famous in August 1846, when the Donner pioneer family joined the Reeds
and several other families migrating to the West on what was supposed to be
a shortcut across this desert. Instead, they encountered a series of setbacks,
including a lack of freshwater and thick salty clay sediments that proved
heavy going for their ox-drawn wagons, all of which took a toll. h e result of
using this shortcut (the so-called Hastings Cutof ) was a delay that put the
migrants in the Sierra Nevada in October, exactly the wrong time to begin a
crossing of this mountain range. h e timing was made worse by the onset of
an early winter with a series of heavy snowstorms. h
e misery that ensued is
now an ingrained part of California's history.
If we step further back in time and observe this same region 15,000 years
ago, the desert was instead part of a vast, deep body of water, which is today
called Lake Bonneville. Had the early pioneers crossed the region during
that time, they would not have been contending with empty, endless deserts;
rather, they would have been following seemingly endless shorelines that
bordered gargantuan lakes. Today, the Great Basin has some sizeable lakes
and playas, including Pyramid Lake in Nevada, Owens Lake in California,
and the Great Salt Lake in Utah. Drawing on a variety of lines of evidence,
both from within the lake-bed sediments and from the geomorphic traces of
ancient shorelines that ring the playas along the slopes of nearby mountains,
it is clear that, at times in the past, the Great Basin supported vast lakes that
were not only hundreds to thousands of square miles in area (for example, the
Great Salt Lake's ancestor, Lake Bonneville, was close to 30,000 square miles
at its peak) but also very deep. At one time, Lake Lahontan, in northeastern
Nevada, was one of the largest lakes in North America. With over 10,000
square miles in area, this lake once encompassed modern-day Walker Lake
in the south, Pyramid Lake on its western edge, and Winnemucca Lake on
the northeastern edge. Yet another large lake, Owens, is found in southeast
California. Today, this lake is completely dry, but it once covered an area
close to 400 square miles. h
ese lakes expanded and contracted through the
ages with changing climate.
Enormous lakes were, in fact, a common feature on the glacial landscape.
But, in contrast to the colossal glacial lakes that formed farther north along
the southern edges of the melting continental ice sheet, it is thought that the
lakes of the Great Basin grew to such a great size as the result of both higher
