You first have access to a quarry when the HQ is at level 7. The quarry produces stone. You can use stone to build and upgrade other buildings. As you upgrade the quarry you increase both the amount of stone the quarry can hold and the amount of stone you produce per hour. You also gain Xp points to boost your city level. There is a total of 2 quarries to gain during the game. You will be able to access the second quarry when the HQ is at a high enough level. In order to upgrade the quarry, the HQ needs to be at a certain level.