What was it about aliens and quarries? It seemed like anytime alien races came to earth, they made straight for the nearest quarry, preferably disused, and set up base there. Maybe abandoned quarries reminded them of home; there were a lot of bleak, rocky worlds in the universe. The Doctor had visited a fair few in his travels; there was no accounting for taste.
On the other hand, battling the enemy in a remote quarry had its advantages. Fewer people around to get hurt or captured; damage was restricted to rocks rather than buildings.
Best of all, hardly anyone noticed.