Geoscience Reference
In-Depth Information
changes. In other words, the climate became more variable. From the coastal
ocean to the inland Great Basin, the evidence all points to a less stable cli-
mate. Along the coast, for instance, in the Santa Barbara Basin, sea surface
temperatures, upwelling, and the thicknesses of the sedimentary layers show
greater variability. Pollen separated from marine sediment cores taken of the
Central California coast suggests that vegetation growing in those regions
began to show more rapid l uctuation from wetter to drier species starting
about 3,400 years ago. Inland at Pyramid Lake, in western Nevada, studies
of pollen and plankton (diatoms) from lake sediment cores also exhibit an
increase in climate variability at er 3,500 years ago. h is increased variability
may be due to an increase in the frequency of El Niño events that appears to
have begun at that time. A more detailed discussion about changes in the
ENSO and other climate cycles will be given in chapter 11.
h e wetter and cooler climate of the Neoglacial gave way to a period of
drying conditions at er about 1,800 years ago. Was this change favorable or
unfavorable for our intrepid mound builders? As we shall see in the next
chapter, there is evidence that these mound dwellings, as well as other
Native American settlements in California and elsewhere in the West, were
abandoned during this warmer and drier period, perhaps in response to the
change in climate.
