I went back to Dripping Springs Ranch Park yesterday after the city office let me know that the tree and limb drop-off had reopened and that mulching was about to start. The operation was in full swing when I arrived shortly after lunch with this amazing machine chewing through the pile from one side while folks dropped their truckloads of broken limbs and branches on the other.
The machine in question is a DZH4000 Horizontal Grinder and its 755 horsepower can mulch up to 120 tonnes of wood brush per hour. It looked to have turned about a third of the pile into sawdust in the 5 hours or so that it had been running yesterday morning.
For the technically inclined...