Ornamental grasses do something no other plant does: they move. In a valley with this much wind that is not a small thing — a planting with grasses in it is never entirely still, and the difference between that and a static bed is most of why some landscapes feel alive.
They are also among the toughest plants on this list. A great many of the good ones are prairie and steppe plants adapted to exactly this — alkaline ground, hard sun, a long dry stretch in late summer, and cold. Established, most of them want less water than almost anything else here that still looks like something.
Their best season is the one most plants have given up on. Grasses carry through fall as the seed heads mature and the foliage turns, and they hold into winter — standing tan and catching snow when the beds around them are bare. That makes them the backbone of the January view, and it is the reason the right time to cut them back is late winter, just before new growth, rather than at fall cleanup.
One thing to get right before anything is planted: clumping or running. A clumping grass expands slowly from one crown and stays where it was put. A running grass travels by rhizome and ends up in the lawn and in its neighbors. Both are sold as ornamental grasses and they are completely different commitments. In a mixed bed, the clumping ones are the only safe answer.