What is the meaning of 3 or 4 rocks stacked on top of each other?

A stack of three or four rocks typically indicates the location of a trail, a place for meditation, or to indicate a memorial. These stacks have navigational meanings, such as marking turns or forks in a trail or path. The structure is also known to have various spiritual meanings.

A stack of rocks is called a cairn. According to AMC Outdoors, cairns have been used to mark trails for thousands of years and are still in use today. Some religious traditions use them as parts of rituals or to mark spots for a person to stop and meditate. Archaeological evidence shows that some ancient Native American cultures used rock cairns to mark burial sites.