In answer to your request for details: (1) rocks are rounded, about the size of a fifty-cent piece (NOT pebbles) (2) layered a good 3 - 4 inches deep, unfortunately (3) drive is FLAT (4) my spouse oversaw this project, so we are not in a position to demand they come back with smaller and fewer stones (5) located in Michigan, so getting stuck this winter is a real concern. Again, ideas are welcome. Thank you!