Palo Alto - sediments (bay mud)

Accumulation of bay mud west of San Francisco Bay at the west end of the Dumbarton Bridge.

Young sediments (Quaternary, or less than 1.8 million years old) have mostly not had time to be transformed into rock, and the youngest sediments (Holocene, deposited since the last period of extensive glaciers and ice fields, or less than 11,500 years old) are usually found in their original environment of deposition. One such Holocene accumulation is that of bay mud (shown as Qhym on the geologic map) which has been deposited on the bottom of San Francisco Bay.

San Francisco Bay was once larger than it currently is, so it is surrounded by extensive flat areas of bay mud. These mudflats have largely been covered with artificial fill, or converted to dry land and salt evaporation ponds by extensive levees.