Final answer:
The granite core of the Sierra Nevada Mountains, estimated to be 150 to 80 million years old, was formed due to the subduction of the Farallon plate beneath North America during the Late Mesozoic era. This process resulted in volcanic activity and the creation of massive granite intrusions, which are now visible as the Sierra Nevada's prominent features.
Step-by-step explanation:
The Sierra Nevada Mountains are primarily composed of granite that was formed through geological processes related to subduction. Specifically, this granite is a product of the subduction of the Farallon plate beneath the North American continent. This happened during the Late Mesozoic era, at the same time the Rocky Mountains were forming. As the Farallon plate subducted, it led to volcanic activity and the intrusion of massive granite batholiths, which are now exposed due to the erosion of the once overlying volcanoes. The topography of the Sierra Nevada that we see today, including iconic landmarks like Yosemite's Half Dome, has been shaped by extensional stress within the last 5 million years, resulting in large fault blocks that form the range's steep face.
The vast granite expanses of the Sierra Nevada did not result from a continental rift, hot spot, transform plate boundary motion, or meteorite impact. These mechanisms produce different geological features and are not responsible for the significant granite formations found in the Sierra Nevada. For instance, hotspots, like the Yellowstone hotspot, lead to volcanic activity and can form calderas, while transform plate boundaries, such as the one between the North American and Pacific plates, typically result in earthquake activity along strike-slip faults.