Park at the Millville post office.  Begins and ends with very windy 15 mile flatish stretches, with plenty of climbing and a few fun descents in between.  You're going to want about 3L of water in nice weather, more if it's hot.  There's a small general store in Whitmore and purportedly another one in Oak Run but that would require a detour from the route.  The surface is very good the whole way but shoulders are often narrow and rough.  Luckily there's not much traffic.

PLEASE NOTE: Much of Shingletown Ridge Road is unpaved.  It is mostly smoothish and hard, but you'll want to go very slowly on a road bike.