Geoscience Reference
In-Depth Information
may have taken generations, probably as people followed the seasonal migra-
tions of animals such as caribou and bison.
Upon their arrival in the new world, people would have found plenty of
food, as well as predators such as saber-toothed tigers, and rapidly chang-
ing habitats. Around 10,300 years ago, the gradual warming trend that had
marked the previous several thousand years in the West suddenly ceased and
the climate deteriorated. For the next several hundred years, glacial condi-
tions returned, a period known as the Younger Dryas. As suddenly as that
period started, it ended, and the warming resumed, marking the beginning
of the Holocene (see i gure 16B). Melting glaciers once again sent water rush-
ing into the sea, raising the level of the oceans worldwide by nearly an inch a
year. h e rate of sea level rise was quite high until about 6,000 years ago; by
then, the rising seas had l ooded what had been coastal river valleys, forming
the bays, estuaries, and wetlands that are part of our modern coastline.
vast ice age lakes in the great basin
Climate scientists have learned a great deal about deglaciation (a period of
rapid climatic warming and melting ice sheets) by studying enormous lakes
in the Great Basin. h e Great Basin is a region in the heart of the American
West that extends across the states of Nevada, Utah, Oregon, and into
Colorado, bracketed on the west by the Sierra Nevada and Cascade ranges,
on the north by the Wallowa Mountains, and on the east by the Rocky
Mountains. h e region comprises a series of linear mountain ranges and
basins that formed over millions of years of tectonic movement between the
Pacii c and North American plates, causing extensional pulling and shearing
of the landscape. Today, it is predominantly a high desert region, beautiful
and stark with sagebrush-dominated desert valleys alternating with linear
mountain ranges. h e Great Basin is so named because of its hydrology: the
region's rivers have no outlet to the ocean, instead terminating in the lakes,
vast playas, and dry lakebeds of this giant basin.
Climate in this region today is semiarid, with mild winters, warm sum-
mers, and little precipitation. Like the West Coast, precipitation is brought
to the Great Basin mostly during the winter by westerly winds carrying mois-
ture from the Pacii c Ocean. Rain and snow from the mountain peaks feed
the rivers that drain into the Great Basin, but freshwater is limited, not in
sui cient supply for its growing population.
