Early excavation of mounds

Former US President and drafter of the Declaration of Independence, Thomas Jefferson, was among the first to document the excavation of Native American burial mounds near his home in Monticello, Virginia.  In the decades that followed, burial mounds were often excavated not for cultural enlightenment, but for "treasure" hunting. 
Events leading up to the passage of the NAGPRA Act
Slack Farm Mound Site - In 1987, significant desecrations of a 500 year-old Native American burial mound located in Uniontown, Kentucky, were brought to national attention as the human remains of indigenous peoples were carelessly thrown to the side as the site was combed over for valuable Native American relics
Dickson Mounds  - From 1927 through 1992, a local family in Lewistown, Illinois maintained a private museum displaying artifacts and the uncovered skeletons of 237 Native Americans that were excavated on their farm. The museum was closed by the Illinois Governor (Jim Edgar) at the time for the desecration. This incident again brought international attention to create laws that would protect the remains and cultural relics of indigenous cultures.
History of North American Moundbuilders

Mound Builders were prehistoric American Indians, named for their practice of burying their dead in large mounds. Beginning about three thousand years ago, they built extensive earthworks from the Great Lakes down through the Mississippi River Valley and into the Gulf of Mexico region. These mounds, many of which survive today, consisted of several hundred tons of dirt, clay, and stone, and were built on a large scale in spite of the fact that the builders had no beasts of burden and did not use the wheel. The Adena people were one group of Mound Builders. They arose in the Ohio River Valley around 400 BCE They were hunters and gatherers, and also fished. They settled in villages scattered over a wide area. The largest Adena mound is the Grave Creek Mound at Moundsville, West Virginia; it measures 900 feet in circumference and 70 feet in height. Scholars believe that as the Adena traded with other groups of American Indians, the practice of mound-building spread. Other Mound Builders were the Hopewell and the Mississippian people. The Hopewell were hunters and gatherers but they also cultivated corn and squash. They settled in the Midwestern United States, where their burial mounds can still be found; the largest site is in Newark, Ohio. Objects such as shells, shark teeth, and volcanic glass discovered in the Hopewell earthworks reveal that they traded with distant tribes. This trade network collapsed about 1,500 BP and the Hopewell died out. The Mississippians, who settled in the Mississippi valley and in what is today the southern United States, were the only Mound Builders to have contact with the Europeans. Their culture emerged about 1,300 BP and lasted into the 1700s. The Mississippians were farmers and raised livestock. In addition to their mounds, the largest of which is found at Cahokia, Illinois, they built cities, which were among the earliest in North America. Since many of their earthworks (c. 1200–1500) include temples atop the mounds, the Mississippians may have traded with the Indians of Mexico (such as the Aztec or Maya), and were influenced by them.