Jaime Hernandez: In 1999 the Mint provided General Mills with 5,500 Sacagawea dollars to promote the new coins. General Mills placed one Sacagawea dollar inside every 2,000th box of Cheerios. In 2005, collector Tom Delorey discovered that some of these 5,500 Sacagawea dollars bore an unusual design on the reverse. Each of the "Cheerios" dollars featured detailed veins in the eagle's tail feathers, details that were lacking on regular Uncirculated and Proof Sacagawea dollars.
After the initial discovery, the hunt was on. Collectors did not become aware of the significance of the "Cheerios" dollars until well after the cereal boxes had been distributed, and it is likely that the vast majority were spent by their unsuspecting owners. Estimates of the surviving population are very low, ranging in the couple of dozens. As of November 2012, PCGS had certified only nine examples in all grades.