Public utility locates are done by companies that are hired by facility owners to locate their lines. In Colorado, all public utility locates are coordinated under the 811 Dispatch Center. If you are digging, you are legally required to call 811, or to fill out their form at
https://colorado811.org/. 811 will notify all public utilities in your area, and those public utilities are legally required to respond within 2 business days of your request. They are required to do this either by putting paint on the ground, or notifying you that you are in the clear.