Sandhills migrate all the way from northern Canada down to the deserts in AZ & elsewhere like the Bosque del Apache in NM. So you're liable to see them resting anywhere in between.
When I was hunting caribou in the NWT, we saw 1000s of them, and the same on my moose hunt in northern BC. At the latter, a big flock would stop on a tundra covered hill top & spend the night, then leave in the morning. And boy, do they make a racket, both when flying over & while feeding.
Wait til you spook a pair trying to sneak across a meadow, they will do a scraping run while calling, loud enough to alert the whole area.
They like the high mountain meadows , we've seen them at 9,000 ft.