I don't have the route but, surprisingly IMO, setting the graphics option to Highest does not one of the sliders to maximum. The slider controlling the Level of Detail shown in the game is set to one below the end-stop so any asset whose LOD is set to 1 still won't show up, only 2 and above, unless you manually move the it. Alternatively, go into the World Editor, move to the Dawlish area and move your mouse pointer over the area you're expecting the sandstones to be. If LOD level is the problem they'll show up under the pointer. Double-click on them to show the fly-out box on the upper right of the screen and raise the LOD setting manually and save the changes.