A mesa (Spanish for table) is an isolated hill with a flat top and steep cliff like sides, at the base of which are the remains of the weathered rock that gives it its distinctive shape.
Mesas are formed by weathering and erosion of horizontally layered rocks that have been uplifted by tectonic activity. Variations in the ability of different types of rock to resist weathering and erosion cause the weaker rocks to be eroded away, leaving the harder rocks higher than their surroundings.
A mesa closely resembles a butte, though larger.
Because of their distinctive shapes, mesas and buttes are frequently used as landmarks.
The rule of thumb in differentiating the two is that a mesa has a top that is wider than its height, while a butte has a top that is narrower than its height.
Chambers Pillar in the Northern Territory is a butte. Mount Conner along the road to Ayers Rock in the Northern Territory is a mesa.