Doesn't "cea mare" mean "the most beautiful"; e.g., "The region is the most beautiful"?
(not native, but I guess)
cea mai mare = the biggest
cea mai frumoase = the most beautiful
but maybe cea mare = so big, this big, uniquely big
So it is not a region that happens to be big among other things (regiunea mare și uscată) but the region known for being the big one like the "The Great Region" (regiunea cea mare).
A bit like Alexander the Great...?
Romanian natives, please correct me!
It'a bit of a strange sentence, but I think you are close with the region that is known for being big. I would translate "regiunea cea mare" literally as "the region that is big" or more naturally as simply "the big region."