Thanks for all the suggestions- while the gravel I have in the run is rounded, around 1/2-3/4 inch in diameter, I am leaning towards excavating some of it so there is a base layer for drainage and topping it with builder's sand- there is a building supply place down the hill from where I live, so it is handy to stop by on the way home from work. They are willing to sell me gravel and sand by the 5 gallon bucket for a dollar/per bucket- not too cheap, compared to bulk, but cheaper than Home Depot, and I don't have to pay delivery charges or rent a pickup! The guys at the building yard will even fill up my buckets and load them up into my little Ford Focus for me ;-)
The sand I get has bits of small stones and mixed diameter sand, not too fine. I have been putting a tray in the brooder for my chicks, and they love dustbathing in it, and the fact that poop is so easy to pick out from the sand with a kitty litter scoop is another reason why I am leaning towards having sand on top of gravel.
Now if only I know the breed of my 2 mystery chicks- they turned out NOT to be GLW.