It depends on what industry your company is in. California wage and hour law has many layers. Primary are the Labor Code, and the regulations - or "Wage Orders" - enacted by the Industrial Welfare Commission (IWC). If you check the IWC's web site, you will see that it has 17 "Wage Orders" for different industries and occupations.
That being said, most of the Wage Orders provide: "Each workday an employee is required to report for work and does report, but is not put to work or is furnished less than half said employee’s usual or scheduled day’s work, the employee shall be paid for half the usual or scheduled day’s work, but in no event for less than two (2) hours nor more than four (4) hours, at the employee’s regular rate of pay, which shall not be less than the minimum wage."
So if your employees typically work more than four hours per day, and you call them in for a one hour meeting, you have to pay them for half of their usual shifts, but in no event less than two or more than four hours.
I would recommend that you speak with an attorney who helps employers comply with the wage and hour laws. You can call your local bar association for a referral.
Disclaimer: This answer does not constitute legal advice and cannot be relied on, as each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.