It was legal to send you home.
Whether or not you are due pay for that time depends on whether you are exempt or non-exempt. If you are non-exempt, you are never legally entitled to be paid for time you did not work, no matter what the reason, unless there is a legally binding contract that specifically says otherwise.
If you are exempt, you cannot be docked for the time but you can be forced to use vacation or other paid leave for it.