Walking up Causey Pike from Buttermere, I noticed that the pebbles on the path changed colour - from red to white - as the summit was approached.

Above: red rocks from the south east face of Causey Pike.
Below: white rocks from the north west face of Causey Pike

Apparently the Causey Pike fault, which runs from near Ennerdale Bridge to Troutbeck passes through this area, with the Ordovician Skiddaw group (Kirk Stile Formation) to the north and the Buttermere Formation to the south - see here for (much) more detail…