OH Me lets see now. First thing is i've never done anything like this before and it was all guess work.
ROCKS: The large one came out of the wife's garden--Others from the driveway--next smaller rocks are clay floor dry also used as cheap kitty litter and the smallest is sifted floor dry through a flour sifter.
SAND: Is silica sand for a sand blaster which is a fine white sand and sand I bought from Hobby Lobby that is really fine sand that comes in a jar. Both work well for scale,not like regular sand used in construction.
Shape your base sand and rocks then make a mixture of white glue and water. Use a spray bottle and soak the ground work down to hold it all in place when dry.
Then two shades of acrylic sand colored paint applied to give the ground some variation in color and paint the rocks too,the large rock was already the right color.
Let the paint dry. I had different colored earth and sand chalks/pigments so i put little patches of that here and there.
There might be a better way but I wasn't told about it.
There you go,hope this might be of help to you.
Tony lee