The lower Stanislaus River watershed comprises only about one-tenth of the total area and is used mainly for agriculture (61 percent) and urban development (34 percent), with minimal open space. Major communities near the lower river include (from upstream to downstream) Copperopolis, Knights Ferry, East Oakdale, Oakdale, Riverbank, Escalon, Salida and Ripon. The long lower river has been modified extensively not only by water diversions, but by channelization and levee construction to drain wetlands and prevent floods. Most of the natural floodplain no longer exists, and about half of the former riparian habitat has been lost. The river bed has been subjected to extensive gravel mining (mostly for construction purposes), with an estimated 6.3 million yd3 (4.8 million m3) extracted between 1939 and 1999.