Snake Rivers
Yes.
The vegetation cover is sparse. Grasses dominate the landscape. Red grass grows in bush velds. In the high velds acacia and maroola are seen to be growing.
The adverb is mainly. It modifies the verb "drain" to say that the rivers do not entirely drain into the valley.
work
-20degrees
Gulf of Mexico
Columbia and the Snake Rivers
All rivers drain into oceans.Although, due to humans drawing huge amounts of water for our cities, some rivers dry up before they reach the see nowadays.
-20degrees
nile river
the Magdalena and Cauca
Lena River