Trail Rock Cairns Images by ScenicNH Photography LLC Rock Cairns: A rock cairn is defined as a pile of rocks that marks the location of a hiking trail. They vary in size from one foot to massive piles of rocks. Many rock cairns in the alpine zone of the Presidential Range are impressive eye-catching pieces of art. They are found throughout the White Mountains of New Hampshire and make great photo subjects. Above is a slideshow of rock cairns found ...