When Moses failed to come back down the mountain right away, the people went to Aaron. "Look," they said, "make us some gods who can lead us. This man Moses, who brought us here from Egypt, has disappeared. We don't know what has happened to him."
So Aaron said, "Tell your wives and sons and daughters to take off their gold earrings, and then bring them to me."
All the people obeyed Aaron and brought him their gold earrings.
Then Aaron took the gold, melted it down, and molded and tooled it into the shape of a calf. The people exclaimed, "O Israel, these are the gods who brought you out of Egypt!"
When Aaron saw how excited the people were about it, he built an altar in front of the calf and announced, "Tomorrow there will be a festival to the LORD!"
So the people got up early the next morning to sacrifice burnt offerings and peace offerings. After this, they celebrated with feasting and drinking, and indulged themselves in pagan revelry.