Most of the dales in the Yorkshire Dales are named after their river or stream (e.g., Arkengarthdale, formed by Arkle Beck). The best-known exception to this rule is Wensleydale, which is named after the small village and former market town of Wensley, rather than the River Ure, although an older name for the dale is Yoredale.
In fact, valleys all over Yorkshire are called “(name of river)+dale”—but only the more northern Yorkshire valleys (and only the upper, rural, reaches) are included in the term “The Dales”. For example, the southern boundary area lies in Wharfedale and Airedale. The lower reaches of these valleys are not usually included in the area, and Calderdale, much further south, would not normally be referred to as part of “The Dales” even though it is a dale, is in Yorkshire, and the upper reaches are as scenic and rural as many valleys further north.