I would say that in very fast moving water such as in a river, the cobble size could be transported because cobbles are 64-256mm so are quite big and in a quiescent stream won't move much but in a freshet say in a steep mountain stream they can be rolled along such as I observed in the local streams at a mining town during the Hurricane Fifi in Honduras in 1974.
The Ethiopian highlands are a great mass of the rugged highlands in the Ethiopian that are situated around the horn regions and is the largest continuous elevated areas with a surface area of about 1,500 m and is also called the roof of the Africa due to the second-largest areal extent and is geologically 75 million years old.
