The English landscape artist J. M. W. Turner was a frequent visitor to the area, and his sketch of Thornton Force in 1816 is currently part of the Tate collection.

[2] From the caves below Keld Head, water flows and combines with Kingsdale Beck to form the River Twiss.

It flows south over Thornton Force and Pecca Falls and through woodland to join the River Doe at Ingleton.

[4] In its upper part, the river flows through a valley carved into horizontal beds of Carboniferous Great Scar limestone.

The Ordovician strata influence the character of the steep and narrow Swilla Glen and its waterfalls until, just north of Ingleton, the river crosses the Craven Fault and onto Carboniferous Limestone once again.