Sydney’s geographic landscape is as diverse as its vibrant culture, with the city nestled on a submergent coastline where rising ocean levels have flooded deep rias. This coastal basin is bordered by the Tasman Sea to the east, the Blue Mountains to the west, the Hawkesbury River to the north, and the Woronora Plateau to the south. The city's topography spans two distinct geographic regions: the relatively flat Cumberland Plain to the south and west, and the steep, dissected Hornsby Plateau to the north.
The southern flatlands of Sydney were the first to be developed, while the northern suburbs only saw significant growth after the construction of the Sydney Harbour Bridge. Sydney’s coastline is dotted with over seventy surf beaches, with Bondi Beach being the most famous. The Nepean River flows along the western edge, becoming the Hawkesbury River before reaching Broken Bay. The city's major water sources are located along its tributaries, with the Parramatta River draining much of the western suburbs into Port Jackson, while the southern areas are drained by the Georges River and Cooks River into Botany Bay.
Sydney's expansive geography is difficult to define with precision, but the Australian Statistical Geography Standard defines Greater Sydney as spanning 12,369 km², incorporating the local government areas of Central Coast, Hawkesbury, Blue Mountains, Sutherland Shire, and Wollondilly. Within this region, the City of Sydney itself covers about 26 square kilometers, stretching from Garden Island in the east to Bicentennial Park in the west.
The city's geology is dominated by the famous Sydney sandstone, primarily formed during the Triassic period, with layers of shale and fossil riverbeds embedded within. The Sydney Basin, which was created in the early Triassic, is part of a larger coastal bioregion marked by cliffs, beaches, and estuaries. The rias, or deep river valleys, were formed millions of years ago and later flooded, giving rise to the stunning Sydney Harbour, a natural feature that defines the city’s landscape.
In addition to sandstone, Sydney’s soils include sandy types derived from the Hawkesbury sandstone and clay from shales and volcanic rocks, with some soils being a mixture of both. One significant geological feature in the region is the Wianamatta shale, found in western Sydney, which dates back to the Middle Triassic period. This shale is associated with a large river delta and is made up of fine-grained sedimentary rocks like mudstones, ironstones, and siltstones, with some sandstone units.
Sydney’s geography and geology, from its harbors and beaches to its mountain plateaus and river valleys, continue to shape the city’s development, offering both challenges and opportunities as it grows and evolves into a modern metropolis.