The main ground cover areas have now been painted and textured. After building up the surface with DAS modelling clay and then sanding it smooth, I added some light texture from fine sand which was glued in place with a mixture of PVA glue and Matt Medium. Later I painted the ground cover with various acrylic paints applied in light washes with some opaque areas 'splodged' in.
The concrete wall section to the left (see this post for more details) has been glued in place.
The final detailing, the lightly laid ballast around the 18 inch narrow gauge track was modelled from some small clay bricks (part of a build-it-yourself house kit) which I ground up in a mortar and pestle before sprinkling it along the route of the track and sealing in place with PVA glue and Matt Medium.
It was good to see the baseboard covered after so long.