It depends on whether you did it on purpose or with gross negligence. California's wage orders state that an employer may not deduct for loss of equipment unless it was due to an employee's "dishonest or willful act or by the gross negligence of the employee."
Your employer cannot deduct money from your paycheck for mistakes that are honestly or
negligently made, under California Labor Code §2802.
California Labor Code 2802 says that "An employer shall indemnify his or her employee for all necessary expenditures or losses incurred by the employee in direct consequence of the discharge of his or her duties, or of his or her obedience to the directions of the employer, even though unlawful, unless the employee, at the time of obeying the directions, believed them to be unlawful."
So the question is whether the loss was "necessary" and "in direct consequence of the discharge" of your duties. That's why the wage orders talk about purposeful misconduct or gross negligence. The wage orders are not the "end all, be all" of the law, though, and are often treated just as guides by the court. This statute is still open to quite a bit of interpretation in court, and probably will continue to be developed in the case law.
The bottom line: 99% of the situations are obvious in how the employer should treat losses caused by employees, but if there is ever a question, a lawyer should be consulted.