Ranches vary. Hell, the terrain varies on the same ranch pretty good in places. Especially one with half a million acres or more.

Syc, cattle don't stay by the river, because if they did, there wouldn't be anything but a muddy trickle through the desert.

Nearest river to the desert BLM that I ranch is the Rio Grande about 120 miles away. So, they put in pretty sophisticated water systems that feed troughs through the area. Pastures are usually separated by where the water is in relation to graze. A pasture fence does it's job by keeping cattle out of a certain area, as much as it does by confining them to a given area. The water systems are indeed what lets ranchers take advantage of large areas of desert, and the cattle are indeed spread out on the desert.

The water systems take constant monitoring and maintenance. All you have to do is neglect checking and let a pasture run dry of water in the desert, and in a couple of days you have enough dead cattle laying around to eat your profits for the last 5 years.

If what holds true about most of the West, the bottomlands and river bottoms were homesteaded and deeded, while the vast stretches of desert were where most of the grazing permit lies. Even in the mountainous areas, you see the valleys and creeks as being deeded, and the high mountain ranges as being natl. forest lands.

The deeded lands along the rivers are usually used for growing hay or other farm use that feed the cattle in the times when there is not enough graze, like in winter. That land isn't used to graze cattle much, because there are better productive uses for it.

Molɔ̀ːn Labé Skýla!