All that remains of them to tell their history is a
series of interrupted fragments of channels, mostly choked with gravel,
and buried beneath broad, thick sheets of lava. These are known as the
"Dead Rivers of California," and the gravel deposited in them is
comprehensively called the "Blue Lead." In some places the channels of
the present rivers trend in the same direction, or nearly so, as those
of the ancient rivers; but, in general, there is little correspondence
between them, the entire drainage having been changed, or, rather, made
new. Many of the hills of the ancient landscapes have become hollows,
and the old hollows have become hills. Therefore the fragmentary
channels, with their loads of auriferous gravel, occur in all kinds of
unthought-of places, trending obliquely, or even at right angles to the
present drainage, across the tops of lofty ridges or far beneath them,
presenting impressive illustrations of the magnitude of the changes
accomplished since those ancient streams were annihilated. The last
volcanic period preceding the regeneration of the Sierra landscapes
seems to have come on over all the range almost simultaneously, like the
glacial period, notwithstanding lavas of different age occur together in
many places, indicating numerous periods of activity in the Sierra
fire-fountains.
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