The land forms the interface between the Earth’s crust and its atmosphere. Its physical form – the landscape – includes rock, soil, vegetation, water and structures built by people. ACT landscapes consist of rugged timbered mountains in the south and west (uplands), and hill and plains country in the north and north-east. Approximately 60% of the territory is hilly or mountainous. The flatter northern plains and hill country contain most of the urban landscape.

• The uplands occur at altitudes of 800 m to 1912 m above sea level, lying mainly on erosion-resistant, ancient sedimentary rocks and granite. Flooding has deposited sediments in many of the river valleys.
• The rolling or undulating hills country generally lies between 600 m and 900 m above sea level, across moderately weathered rocks in the north-eastern part of the territory and along the eastern parts of the Murrumbidgee corridor in the south.
• The plains are in the north of the ACT at between 550 m and 650 m above sea level. They occur on readily weathered rocks and on stream sediment surrounding isolated hills and ridges of erosion-resistant rock such as Black Mountain and Mount Ainslie.

ACT soils are highly variable, with most being infertile. The main soil types are lithosols, gradational soils and duplex soils.

• Lithosoils are characterised by shallow stony profiles overlying rocky parent material in the south and west of the ACT. These soils are nutritionally poor and on steeper slopes are liable to erosion when native vegetation is removed or they are mechanically disturbed.
• Gradational soils have profiles that show a gradual increase in clay content with depth. They are common in the Cotter River catchment and in the north-east, and are the principal soil types under the limestone plains of old Canberra. These soils are deep and relatively fertile. Those on the north-east plain are relatively resistant to erosion. Gradational soils on
  steeper slopes erode if the land is cleared.
• Most of the ACT and its settled areas have duplex soils, characterised by a distinct change in particle size at a depth of 15–30 cm. The topsoil is light in colour, coarse textured and often sandy. It is fragile and, if cultivated or overgrazed, becomes hard setting and relatively impermeable so that rain runs off and can form erosion gullies. Subsoils tend to be reddish or yellow clays that may shrink and swell as water content changes, sometimes damaging infrastructure. These soils often contain sodium salts, so that they are dispersible if exposed. Much of the turbidity of Canberra’s lakes after heavy rain is caused by erosion of these soils.