Tundra biomes are somewhat common and have very unique attributes. Each Tundra biome has a chance of being either mountainous or relatively flat. Both versions of this biome have grass but lack trees. The mountainous version comes with the addition of snow-capped peaks, while the flat version includes sand and water.
The grass is a variant of the 'Grass' block called 'Grass Tundra'.
It's a rather bad choice to start a colony here because of the fact that Tundras are barren wastes with no sources of lumber, food or water. However, the lack of nearby recources is somewhat compensated by how easy it is to clear space for your settlement and how open your guards sightlines are. Also it's unique appearance gives a lot to work with - the tundras red grass and clear skies fit well with both a gloomy necropolis, to a reclusive dwarf fortress.