Effigy mounds

"A system of symbols" is the framework upon which a religion is designed.  It is the "webbing," a term we used in class, that provides a group of people with emotional comfort and stability.  In the case of Native Americans thousands of years ago, their effigy mounds and the values from which this practice stems were a clear source of that stability.  This action occurred over many generations, suggesting that their religion was not provoked to change for a long time.  The system of symbols associate with burying the dead and piling a hill of dirt over the bodies was a solid one.
The process itself over time became very specific.  It was originally simple and disorganized mass grave sites in the Copper Age. Steadily, evidence was exposed for later sites in which people were placed in definite positions for their burial.  Often people were buried and re-buried for ceremonial reasons.  In the case of the large mound complex at Hopewell, the intricate log-lined crypts contained very organized piles of bones and space for newer bodies, in addition to repositories to act as "waiting rooms"  for a spot in the crypts.  Some bodies were even cremated, and the mounds were burned and made taller after they were full. Many individuals were laid down with valuable objects and little symbols of animals, which suggests a religious connection to nature.  There were many other rituals associated with dying including smoking and ceremonies that need not be mentioned specifically.

What all these practices amount to is a reasonable theory for religious inclinations of ancient Americans.  They had developed a system of symbols animals, different types of stones, and a death ritual.  The first provided was a way to receive protection in this life and the next.  In the theory of totemism, different individuals would have the separate characteristics of each animal; carnivores could be strong and cunning, herbivores might be agile or patient.  These added supports helped establish a sense that nature was on the Native Americans' side, and that they would have the protection of the same "animal people" of their community.  The obsidian, pottery, and other objects found with bodies in burial mounds told these people a similar story about the order of existence.  Theorized not to be a measure of the deceased's family wealth, the elaborate trinkets were given by many members of the community (generosity was a much more important than maintaining wealth, probably a religious virtue) as offerings for a respected end of life.  The intricate symbols on silver, copper,  pottery, etc would not have been buried with the dead if they had no religious purpose.  Large sites in conical and otherwise shaped forms were not just a funny thing to do in one's spare time, they were a religious commitment done to feel a sense of security in what happens to loved ones post-death.  The Native Americans had developed a system by which they could feel safe in sending people into the unknown, and recognize an order in which different rituals had to occur for a given order of existence.