Wait a week. When all is dry, go over the entire mountain once again with the basic color to match your dirt. For my layout, this is raw umber. If you have a large area to cover, you can put the stain in a squirt bottle and just spray everything. Wait a week.
Some people use India ink instead.
Mix well and apply liberally to the rock casting. Allow the black color to run down into the crevices and cracks of the rock work to accentuate the shadows. Ground cover is not within the scope of this article, but can be applied anytime after the weathering stain drys. Colorado mountains have lots of vegetation, trees, dirt, and ground cover on them. They are not really bare rock.