In Cities: Skylines II (also known as Cities: Skylines 2) we can build a deep open pit stone and coal mine. 
Terraforming
- Place a mine in the selected area
- Extend the mine area to the circular border
- Build a temporary road around it to mark the maximum mine area
- Bulldoze the mine
- Terraform a pit in the middle for the mine building
- Terraform a spiral path to the bottom of the mine four times wider than the gravel road
Road construction
- Place a mine at the bottom of the pit. Click the right-mouse button to rotate the building.
- Place a straight gravel road segment at the front of the mine.
- Build a gravel road from the mine to the surface road on the spiral surface.
Mine area creation
- Stretch the mine area between the road segments.
- Continue the area definition up to the surface.
