I built a base to depict a desert scene and it was simple as using the "glitter technique" from kindergarden/gradeschool in attaching sand to a wooden base.
-Sand base and clean
-Spread white glue (I used Elmers) on base
-Add sand (from local play area; was living in Yuma, AZ at the time)
-Shake off excess
-Repeat as necessary
I'm guessing this should work with regular dirt was well, since white glue dries clear. It's just one option out there. Let your imagination be your guide.
Have fun!
Carl