Gravity :)
what causes it is the mountain slopes
oklahoma's rivers flow south-east
Simply, always downhill, under gravity, its course influenced by the geology of the land it crosses.
south
The Continental Divide (in North America) marks the direction (towards the Pacific or Atlantic and Gulf of Mexico) rivers flow.
Mexico
South
Rivers always flow downhill, regardless of compass direction. It is a myth that rivers "normally" flow from north to south.
yess hehe
Wind!
Rivers can flow in any compass direction, a river will always flow downhill.
they flow west
As with all rivers - Gravity.