As you approach Stenalees from St Austell you will see a Monitor by the side of the roundabout. These are used in the clay pits to direct a high pressure jet of water into the rock face to wash out the china clay. This then is pumped up from the pit bottom through refining processes and settling tanks. Then the clay is dried ready for packing and export.
For the full story of China Clay (Kaolin), from 1746 when it was first discovered by the Plymouth chemist William Cookworthy to the up to date methods of extraction you should visit the museum at Wheal Martyn, which is situated, between Stenalees and St Austell. If you thought that China Clay was only used in pottery you will be in for a big surprise!