Mountain drainage basins are considered, featuring different Configuration and pattern of drainage net and water divides. A hypothesis is introduced which-explains the mechanism of the mountain drainage basin formation as a result of endo- and exogenic processes interaction. The leading role is attributed to relaxation processes in the mountain mass when it appears on the day surface. The pressure release results in a fissure system formation which may be considered a prototype of channel network concentrating surficial and subterranean waters. A river channel is regarded as an independent emergent system created by the principal processes interaction.