Legal Question in Construction Law in California

You have to pay hourly wage AND compensate for use of their vehicle when they use their own vehicle on business. You must not only pay gas but also all the other expenses of operating their vehicle for your company benefit, such as insurance, depreciation, maintenance, etc. Of course you only have to pay that on a pro-rata share for the portion of the employee's total driving that is done for you. The simpler solution is just to pay the current IRS rate mileage for the miles the employee drives, which is a close enough approximation to cover your obligation.