well, there's swale and then there's swale. here's the type of thing a lad's likely to have run into:

There were miles of rolling ridges, rough in the hollows, and short rocky bits of road, and washes to cross, and a low, sandy swale where mesquites grouped a forest along a trickling inch-deep sheet of water.
- The Light of Western Stars, by Zane Grey

sometimes it was like reading T. E. Lawrence, considered in retrospect.