Regarding crushing and screening, Gary McCall, area manager for Hanson Aggregates' San Diego-area operations, says, "Things have not really changed in the last 150 years. You take large rocks and put them in a machine to make little rocks, and then you run that material across something with little holes in it and you sell what comes out. "But particularly with the alluvial deposits," McCall says, "and even here [at the El Cajon quarry], with all the dust control that we use, our screens would blind over. There was, on average, about an hour of production per day spent cleaning screens."
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