I'm not sure whether this 'pass' between Austwick and Helwith Bridge is a named glacial valley, but it's the best route I know from Clapham railway station to Ribblesdale, and hence Pen-y-ghent.
Note it was formed by glaciation of the Craven Fault system, rather than carved by a river – as is typical for limestone, there are no significant surface watercourses (that's a road in the distance, not water).