Geoscience Reference
In-Depth Information
f igu r e 17. Ancient tree stumps exposed in southern Lake Tahoe in the Sierra Nevada,
California. (Photo courtesy of Derrick Kelly.)
enough, evidence of the prolonged mid-Holocene drought was discovered
during a modern drought—the Great Dust Bowl drought of the twentieth
century, which was California's worst multiyear drought in recent times.
Four years at er that drought began in California in 1928, the water level of
Lake Tahoe in the Sierra Nevada had dropped by fourteen inches, exposing
a mysterious clustering of tree stumps sticking up from the water's surface
along the lake's southern shore (see i gure 17). h ese trees attracted the atten-
tion of Samuel Harding, a scientist at the University of California, Berkeley,
who discovered that the trees were large, with trunks upwards of three feet
in diameter, and that they appeared to be i rmly rooted in the lake bottom.
Wanting to know more about these trees, Harding collected eleven core
samples from their trunks. He reasoned that the trees had grown in this loca-
tion for a long time to attain such sizes and, since they were now submerged
in over twelve feet of water, that at some time in the past the lake level had
been much lower. He counted 150 rings in one of the cores, which indicated
that south Lake Tahoe had been dry and below the shoreline for well over a
century. h e site must then have been abruptly inundated with water, drown-
ing the trees fast enough that they were let standing in their current upright
positions.
