Page "Geology of the Yosemite area" Paragraph 13

10 million years ago, vertical movement along the Sierra fault started to uplift the Sierra Nevada.

Subsequent tilting of the Sierra block and the resulting accelerated uplift of the Sierra Nevada increased the gradient of western-flowing streams.

The streams consequently ran faster and thus cut their valleys more quickly.

Tributary streams ran more-or-less in line with the Sierras, therefore not having their gradients increased.

Thus their rate of valley cutting was not significantly affected.

The results were hanging valleys and cascading waterfalls where the tributaries met the main streams.

Additional uplift occurred when major faults developed to the east, especially the creation of Owens Valley from Basin and Range-associated extensional forces.

Uplift of the Sierra accelerated again about two million years ago during the Pleistocene.

However, Yosemite valley was not created by streams or fault lines ( to create a graben valley ), such was suggested by geologist Josiah Whitney.

Glaciers shaped the Yosemite Valley, and can easily be confused with a graben valley.

( Example of a graben valley is Death Valley in California )