I live and fly in the mountains of California all the time.
The first thing to be careful about is wind. In the mountains wind can be very unpredictable and turbulent due to the rougher terrain. It can be calm but as soon as you peek your nose above a ridge it can suddenly be very strong. I would be especially concerned with the mini because it has much lower wind resistance capabilities than the bigger Mavics.
Be very careful with RTH height settings. It is difficult to judge obstacle heights along with the variable elevation.
In the winter I would also be careful about the temperature. The Mini is only specified for operation to 32 F.
Those are the big ones off the top of my head. In general, just be more careful than you would in the flatlands.