The average Sierran lake typically has between 10 and 20 feet of sediments-about one foot of deposition per thousand years. Actually, as Spencer Wood has shown, many of the High Sierra meadows, such as Tuolumne Meadows, were forested up to at least the start of the Little Ice Age, when colder conditions developed and the level of ground water rose, drowning the trees. We can therefore be thankful for the Little Ice Age, for without it we wouldn't have the many meadows from which we can view the snow-clad High Sierra landscape. The view-packed Yosemite Valley meadows are also in existence largely due to the presence of a high water table. The meadows once were much more extensive, covering about 745 of the Valley's 1,141 acres, but they were greatly reduced by humans in part due to the lowering of the water table in order to reduce both flooding and mosquitoes, two problems that plagued early tourism.
Humans locally can be powerful agents of geologic change.
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