On the eastern bank to their left they saw long formless slopes stretching up and away toward the sky; brown and withered they looked, as if fire had passed over them, leaving no living blade of green: an unfriendly waste without even a broken tree or a bold stone to relieve the emptiness. They had come to the Brown Lands that lay, vast and desolate, between southern Mirkwood and the hills of Emyn Muil.
”
–The Fellowship of The Ring, The Great River
During Sauron's first war, he adopted the 'scorched earth' policy and destroyed everything he could find whilst his dark army withdrew from the west. He came upon the gardens of the Entwives and annihilated them.
The Brown Lands are the result of that meaningless destruction, a desolate area scattered with boulders and dead oak trees. The grass here is brown (in case the name could not convey that.) It is covered in scrubby grass and is rather dull. It is extremely similar to the Dead Marshes, another place ruined by Sauron, other than the fact that there is very little water here. The Brown Lands were once home to the gardens of the Entwives; that is, until those gardens were incinerated by Sauron.
Upon entering the Brown Lands you gain the achievement"Barren Wasteland".
Structures
Other than Stone Ruins, there is not one structure to break up the endless monotony of this terrible place. After all, who would want to live here? The Stone Ruins are Stone Brick remnants of the glory of civilizations that once ruled these lands.
Mobs
There are no mobs whatsoever in the Brown Lands. Not even Sauron's Orcs can stand this place.
Vegetation
The grass here is a dull brown, and all the trees here are dead. Boulders dot the landscape. No living things exist in the Brown Lands. Tall grass and its variants are less common here than in most biomes, and flowers are nonexistent.