The region shown in the new HRSC image is located in Mars' northern hemisphere, along the planetary dichotomy boundary that separates the ancient southern highlands of Terra Sabaea from the northern lowlands of Utopia Planitia (see context map). This global boundary is generally characterized by a steep escarpment (or “cliff”), with an elevation difference of around two kilometers between the highlands and lowlands. In some areas, the boundary appears very sharp, while in others – such as the Coloe Fossae region – the transition between “high” and “low” is broad and complex. This transitional zone is known as Protonilus Mensae (see context map). It is marked by knobby terrain that rises from the lower plains and stretches for several hundred kilometers before reaching the flat northern lowlands. The region of Protonilus Mensae is also referred to as “fretted terrain” – a term that describes its eroded, knobby landscape.