The consensus is that it was carved out over 650 million years by the Colorado River.
glacier erosion
The Yosemite Valley is one such valley, but there are many.
Yosemite
A stream shaped valley is usually 'V' shaped. A glacier formed valley is usually 'U' shaped.
A 'V' shaped valley is formed by streams and water action. A 'U' shaped valley is formed by the gouging out of the valley walls by a glacier. A hanging valley is where side valleys are cut across by the main glacier. Hanging valleys often have waterfalls that fall into the main valley over a cliff.
santa clarita valley
Cirques are formed
A 'V' shaped valley is formed by streams and water action. A 'U' shaped valley is formed by the gouging out of the valley walls by a glacier. A hanging valley is where side valleys are cut across by the main glacier. Hanging valleys often have waterfalls that fall into the main valley over a cliff.
A V-shaped valley has been formed by a river. A U-shaped valley has been formed by a glacier.
In cross-section: A 'U' shaped valley is formed from glacial erosion. A 'V' shaped valley is formed by river erosion.
It is a valley glacier
The name of a glacier that has frozen to bedrock is rock glacier. A rock glacier is formed by angular blocks of frozen rock that form in the valley of glaciers.