The photo above is the sand based material that our red and blue greens are made of. The courser sand particles allow surface water to infiltrate the rootzone and then flow into the drainage system of the green. This material allows for a firmer & drier putting surface.
The photo above is a model of the rootzone of a sand based USGA constructed green. Notice that there is drainage pipe surrounded by a gravel layer that allows water to flow downward from the sand based rootzone mix into the gravel and into the pipe and out of the green. This is why USGA greens are firmer and drier.