Other rivers reach the sea, and have dissected a broad near-coast region into plateaus, hills and valleys. Many of the features of the drainage pattern of Australia have a very long history, and some individual valleys have maintained their position for hundreds of millions of years. The salt lakes of the Yilgarn Plateau in Western Australia are the remnants of a drainage pattern that was active before continental drift separated Australia from Antarctica. During the last ice age, sea level was over 100 metres lower than it is today, and rivers cut down to this low level. When sea level rose again the lower valleys were drowned.
Coastal geomorphology is also largely the result of the accumulation of sediment on drowned coasts.
In much of the east there is a characteristic alternation of rocky headland and long beach, backed by plains filled with river and marine sediments. These maps have been produced on an orthographic projection with a 20 degree graticule spacing. All six maps have a centre of view at a location of 83 degress East longitude and 45 degress South latitude. There is a broad continental shelf around most of Australia, bounded by a steeper continental slope, except in New South Wales where the continental shelf is very narrow. The Queensland coast is bounded by a broad plateau on which the Great Barrier Reef has grown in only the last two million years.