The highest post-glacial water-marks are well preserved in all the upper river channels, and they are not greatly higher than the spring flood-marks of the present; showing conclusively that no extraordinary decrease has taken place in the volume of the upper tributaries of post-glacial Sierra streams since they came into existence.

But, in the meantime, eliminating all this complicated question of climatic change, the plain fact remains that the present rain and snowfall is abundantly sufficient for the luxuriant growth of sequoia forests.

Indeed, all my observations tend to show that in a prolonged drought the sugar pines and firs would perish before the sequoia, not alone because of the greater longevity of individual trees, but because the species can endure more drought, and make the most of whatever moisture falls.
Again, if the restriction and irregular distribution of the species be interpreted as a result of the desiccation of the Range, then instead of increasing as it does in individuals toward the south where the rainfall is less, it should diminish.

If, then, the peculiar distribution of sequoia has not been governed by superior conditions of soil as to fertility or moisture, by what has it been governed?
In the course of my studies I observed that the northern groves, the only ones I was at first acquainted with, were located on just those portions of the general forest soil-belt that were first laid bare toward the close of the glacial period when the ice-sheet began to break up into individual glaciers.

And while searching the wide basin of the San Joaquin, and trying to account for the absence of sequoia where every condition seemed favorable for its growth, it occurred to me that this remarkable gap in the sequoia belt fifty miles wide is located exactly in the basin of the vast, ancient mer de glace of the San Joaquin and Kings River basins which poured its frozen floods to the plain through this gap as its channel.