I bought a 10lb bag of floor sweep at the auto store. It’s what is used to soak up spills at a garage and is just clay. I used one of those wire mesh strainers you put in your sink to separate the larger clay bits from the smaller. I just put the ‘large’ bits around then sifted the smaller on top and secured with scenic cement. You could leave as is .. but I would come back with some more zip texturing using the brush technique (load a brush with the tempera ‘dirt’ .. wet where you want it .. like on the horizontal surfaces .. and gently the brush against your finger. You can get really good control doing that).
Since I did this I found another great source for rubble. If you go by the section of your Lowes/Home Depot where they have the patio stone, look for a bag of ‘Paver Base’. My local Lowes’ is decomposed granite. You can’t wrong with a 50lb bag of great scenic stone/rubble for less the $4 a bag!
The difference is that the floor sweep being clay will take stain better then the granite. I like to use both.