e. Supply drop zones may, in general, utilize any of the following types of surfaces: 1. Surfaces containing gravel or small stones no larger than a man’s fist. 2. Agricultural ground, although in the interest of security, it is inadvisable to use cultivated fields. 3. Sites containing brush or even tall trees; however, marking of the DZ and the recovery of containers is more difficult. 4. Marsh, swamp, or water sites, provided the depth of water or growth of vegetation will not result in loss of containers.