She was in the hollow of an old watercourse.

They now went on foot, and steadily climbed the steep hillside by the bed of an old watercourse.

The tunnel narrowed and the old watercourse dropped almost straight down, varying only slightly as it twisted this way and that.

Then, taking advantage of an old watercourse, it turned to the right, and when Compton recovered the track he had lost touch with Venning.