Subsidence in the Long Beach Harbor area, California

Surveys and other observations in the area of Long Beach Harbor, California, indicate a general subsidence over a large area. Over the near-by plain to the north and east of the harbor, this subsidence averages a few tenths of a foot over a period of about 20 years. In this larger field of subsidence there is a localized area within which the depression of the surface amounts to several feet, reaching a maximum of more than 4 feet in the region of the Inner Harbor. This area of maximum subsidence, when contoured according to available level data, coincides remarkably with the productive area of the Wilmington oil field. It is also highly significant that the subsidence, as indicated by tide-gauge records, first became notable in 1937, shortly after the beginning of the development of the field.