Map from the U.S. Geological Survey
Do you see any colored squares near Yosemite Valley in the map at left? Each square represents an earthquake recorded by seismographs in the past week. Earthquakes often occur near Mammoth Lakes, to the southeast of Yosemite, but not many happen in the Park itself.
Many earthquakes that do occur in Yosemite are caused by rocks breaking in the crust below us as part of the process of building mountains. Some are more enigmatic. One area, near the Clark Range to the southeast of the Valley, frequently has earthquakes as deep as 30 km (about 18 miles) below sea level. Earthquakes deeper than about 15 km (9 miles) are uncommon in California and Nevada.
Occasionally other events will produce seismic waves. For instance, rockfalls will generate seismic waves that can be detected far away. The large rockfall just south of the Happy Isles Nature Center in 1996 was as big as a magnitude 2.1 earthquake and was seen on seismometers 200 km (120 miles) away.
Press to learn more about the Glacier Point rockfall from a seismologist's viewpoint