Authorities took down about 100 tents and arrested 70 people in what the protesters said was a surprise raid, which began shortly after 1 a.m.
Officers surrounded the plaza and gave the remaining demonstrators five minutes to clear out.
Two people threw a chair at an officer, officials said. They were arrested on suspicion of felony assault. Dozens of others were arrested for illegal lodging in the plaza and failure to disperse.
Public works crews started clearing the site littered with plastic bottles, mattresses and chairs.
The tent city was set up in mid-October to protest bank bailouts and economic injustice.
Last month, the city issued an eviction order to the downtown camp and offered protesters an alternate site.
The Associated Press contributed to this report.