[
  {
    "type": "item_group",
    "id": "desertpavement",
    "subtype": "distribution",
    "items": [
      [ "rock", 10 ],
      [ "rock_large", 1 ],
      [ "rock_flaking", 8 ],
      [ "sharp_rock", 8 ],
      { "item": "pebble", "prob": 33, "charges": 1 },
      { "item": "pebble", "prob": 33, "charges-max": 10 }
    ]
  }
]
