CONCORD, Calif. (AP) _ A section of a public park was evacuated Monday because two men were throwing homemade acid bombs from their third-story balcony, police said.

A witness at Ellis Lake Park called police after seeing a two-liter bottle fall from the balcony and explode on the park ground in a caustic mess of singed plastic and grass, said Police Lt. Susan Jones.

The men admitted to police they had been filling soft drink bottles with aluminum strips and muriatic acid, a form of hydrochloric acid used in swimming pools.

``It makes a chemical reaction that explodes, and they were lobbing them off the balcony and watching them explode,'' Jones said. ``They said they had gotten the recipe off the Internet.''

Stephen Braddy, 22, and Michael Vierow, 20, were arrested and charged with several crimes including possessing caustic chemicals and wrongfully possessing chemicals with the intent to destroy property. Their bail was set at $2 million.

Concord is about 30 miles east of San Francisco.