Geoscience Reference
In-Depth Information
Owens Lake in the Owens Valley south of Mono Lake, having desiccated
during the prolonged mid-Holocene drought, also reached a high stand dur-
ing the Neoglacial. In the Sierra Nevada range, Lake Tahoe, which had been
unusually low for hundreds of years during the mid-Holocene, was restored
to its early Holocene high level by about 3,000 years ago. h e lake again
reached the elevation of its sill, causing lake waters to overl ow into what
is now known as the Truckee River, its only outlet. h ese waters l owed
eastward into Nevada, eventually reaching Pyramid Lake, which also reached
a high stand about 3,000 years ago.
Fossilized pollen and plant remains in lakes and meadows in the Sierra
Nevada provide further evidence for cooler and wetter climatic conditions.
For instance, pollen from Lake Moran in the Sierra Nevada shows a shit
in vegetation to cool-adapted i r and pine trees in the region surrounding
the lake, starting around 4,000 years ago. An analysis of charcoal levels in
Sierra lake sediments shows that these levels declined during the Neoglacial,
indicating reduced i re frequency.
california's central valley
More snow and rain in the Sierra Nevada would have caused more serious
l ooding along the rivers draining the range, including the Sacramento and
San Joaquin, as l oodwaters would overtop the banks of the rivers, spread
out over the l oodplains of the Central Valley, and i ll the natural wetlands
that once covered the region. Evidence that major l ooding occurred in the
Central Valley during the Neoglacial period is found in Tulare Lake, located
in the southern San Joaquin Valley. Prior to its recent human-caused desicca-
tion, Tulare was the largest freshwater lake in the American West, receiving
inl ow from the Kings, Kaweah, Tule, and Kern rivers that drain the central
and southern Sierra Nevada. During wet periods, these rivers brought even
more water to the lake, expanding Tulare and its surrounding wetlands.
Paleoclimate researchers analyzed pollen extracted from Tulare Lake sedi-
ments to assess the extent of marshes in the Tulare Lake Basin by determining
the proportion of aquatic plants relative to saltbush, a plant that grew around
the lake's shore. h ese sediment studies, along with shoreline analyses, show
that Tulare Lake experienced a high stand between 4,000 and 2,700 years
ago. h e increased high water and l ooding during this generally wetter
period would have created conditions much like those seen in 1861-62, when
