You're traveling across flat plateau lands and then all of a sudden the canyon just opens up before you.

你正在高原平坦地带走着，突然间峡谷就在你眼前冒了出来。

youdao

When the Banks have been crested, the surrounding land becomes the river, with he water moving across flat land in a sheet, toward whatever is the drainage point.

当河岸的顶部被洪水淹没之时，周围的土地就变成了河流，河水成片地朝着平坦的地势流动，无论何处都成了排水点。

youdao

The road stretched ahead across the flat landscape.

公路向前延伸，经过一片平坦的地。

《牛津词典》

In fourth place: U.S. Route 191 in Utah, which runs across flat scrublands between majestic red cliffs.

FORBES

He said the smell was caused because the sewage did not travel fast enough across the flat land.

BBC: Anglian Water to tackle sewage smell in Ingoldmells

His train was high atop a slender viaduct across a flat valley, and immediately ahead of him was train D3115, moving so slowly that it might as well have been a wall.

NEWYORKER: Boss Rail