Employee was walking the drill pad prior to doing EE's pre shift on the drill. it had snowed 3 inches that evening and EE stepped on the edge of a tire track that caused EE to slip/Trip and fall to EE's knee. when EE came down, EE came in contact with a sharp-edged rock on EE's shin just below the knee cap. we took EE to urgent care where they gave EE 4 Stiches. same day.