In 1904 Mendenhall (1905) made a survey of the ground water conditions in southern California. At the time of his survey the piezometric surface in the area was above sea level, but since that time water levels have declined. During the 1920's, years of rapid development, the water levels declined at an increasing rate. However, because of decreased pumping during the depression years of the 1930's, the levels tended to recover somewhat. During the war years of the 1940's, a large expansion of industry occurred in the area, and ground water withdrawals greatly increased. By 1945 water levels in some areas had declined as much as 70 feet below sea levels In the coastal region this heavy withdrawal and the ensuing dry years rapidly lowered the ground water levels, reversing the normal seaward flow of the underground water to a landward flow.