A mobile machine includes a frame, and a set of wheels supporting the frame. The mobile machine also includes a set of ground-engaging tools mounted to the frame that are movable relative to the wheels to change a depth of engagement of the ground engaging-tools with ground over which the mobile machine travels. A sensor senses the ground surface over which the mobile machine is traveling. The sensor can do this by sensing the position of a ground-following device having a proximal end coupled to the frame and a distal end configured to engage a surface of the ground and follow the surface of the ground as the mobile machine moves in a direction of travel, or by sensing the surface of the ground behind a surface cleaning device that exposes the surface of the ground to the sensor.
