Geoscience Reference
In-Depth Information
WET
DRY
0
1000
Age
(years
before
present)
Mono
Lake
2000
Neoglacial
High Stand
(3700 yrs ago)
f igu r e 20. Ancient levels of Mono Lake
over the past 3,800 years, reconstructed by
using the deltaic sediments of inl owing
streams. Note the high stand 3,700 years
ago. (Based on data from Stine 1990.)
3700
6500 6430 6360
Lake Elevation (feet)
In eastern California, more evidence for a wet Neoglacial climate
was found in Mono Lake in the Owens Valley, to the east of Yosemite
National Park. Mono is a special lake, not just for its unique ecosystems
and fascinating tufa towers but also for its great age: the lake has existed for
over a million years, making it one of the oldest lakes in North America.
h e sediments accumulated beneath Mono Lake therefore contain a rich
archive of past natural history. h e lake is a “closed basin,” meaning water
l ows into it but has no outlet. During dry periods, when the rate of evapora-
tion from the lake exceeds inl ows from direct precipitation and streams,
the water level subsides. During wetter times, when more water l ows
into the lake than evaporates, the lake expands. In this way, Mono Lake
acts as a prehistoric rain gauge. Several lines of evidence indicate that the
lake swelled to its highest known level (or high stand) some 3,730 years ago
(see i gure 20).
