The Mound Builders
Cahokia (related), an Amerindian city the size of Paris, at the time one of the largest in the world c 1000 AD
Poverty Point, mounds from ~2500 years earlier
Rune stones predating our date for European arrival in the US in Mass, Minn, Oklahoma, and elswhere
Great Serpent Mound in Hillsboro, OH
Underground cities beneath Death Valley and Grand Canyon?
Winnemucca Lake Petroglyphs are more than 10,000 years old
The Pedro Mountain Mummy, WY
The Blythe Intaglios, N. Americ's Nazca Lines
Roman coins were found in Texas at the bottom of an Indian mound at Round Rock. The mound is dated at approximately 800 AD. Similarly, an experienced botanist has identified plants in an ancient fresco painting as a pineapple and a specific species of squash – both native to the Americas. The fresco is in the ruined Roman city of Pompeii.
Bonus (not N. America, but giant related)
Tihuanaco, an ancient sea port, 2.5 miles above sea level...
Should get you started OP>>20781977>t. retarded