Removing grass, exposing the nutrient rich soil underneath, is a step to farming. If, however, your goal was to dig deeper while searching for rare minerals, then it would be mining. Considering that you had neither of these things as your intention, what you have done is simply digging.
There is only one tool on the entire Empire capable of that... The Uber_Pick I wouldn't be surprised if that was to become a promo item in the far distant future
