Course: Science Subtest I
Lesson: Earth's Resources
Topic: California's Fresh Water      Page 25 of 39  


One potential problem with intensive use of groundwater is subsidence (sinking) of the land as water is removed from underground aquifers — and even after the water is no longer actively drawn out. In the San Joaquin Valley, more than 5,000 square miles of valley floor sank by at least a foot between 1925 and 1977. In an area west of Mendota, the subsidence amounted to 30 feet!

Dr. Joseph Poland of the United States Geological Survey, standing by a pole that shows land levels in 1925, 1955, and 1977. In 1925, the ground surface was at the marker at the top of the pole. The subsidence was due to groundwater extraction. Source: US Geological Survey