Sorry, Susan. Thought I said earlier. In this case the trough is not a valley a high pass - Rather like what is traditionally called a saddle or a 'coll'. Why it is a though in this case I have no idea but it is on the road that runs from Lancaster to Clithroe. You may be able to see it better on Street Map but you may also be able to zoom in on the co-ordinates using Google Maps

Hope this helps rather than confuses more :-)