I've seen people struggling to know if they've found it, from the above description in the 0.7.6.4 patch notes. But is this it, when it happens to be surrounded by mountains and desert. Is that a deliberate thing that can happen too...?:Added new Grassland ‘Woodland Valley’ sub-biome. This area has rolling grassy hills with a wide flat valley below. Medium to large patches of Trees and Rocks are streaked across the landscape.
The area kind of reminded me or Wales, but more interesting. There's a lovely contrast of colour, with the red mountains rising off the green plain (and dessert lapping at the other side). The grassland was very near circular, too, like a crater, just the right width to be able to see all the sides.
I'd been thinking of suggesting an impact crater mini-biome (you know, like Flagstaff Arizona, with perhaps some mysterious, unique, late game resource to be harvested, to encourage exploring or whatever). But I imagined them much more austere and boring, compared to above.