Here on the Trinity River, the US Fish and Wildlife agency has to dredge portions of the river to remove sediment. They pile up up high enough for hundreds of semi tractor trailer size loads. They give it away "free" for road base, tracks at schools, etc. The sediment is decomposed granite. Slightly courser than "sand" but far smaller particles than pea gravels. I love the stuff, it drains like a champ, you can rake through it and pick up the poo, the pine shavings and the rice hulls and whatever other detritus that is in the hen house and run. Free, Free, Free, and it works better than anything I have ever found.