From the Wikipedia page 
Ulanga District (Mahenge District) is one of the six districts of the Morogoro Region of Tanzania. the administrative seat is in Mahenge. It covers 24,460 square kilometres (9,444 sq mi) of which 4,927 square kilometres (1,902 sq mi) is in forest reserves. Ulanga District is bordered to the north and west by the Kilombero District, to the east by the Lindi Region and to the south by the Ruvuma Region.