Technically my jurisdiction follows the 2016 California Electric Code, but it's mostly just the 2016 NEC.
Table 300.5 lists bury depths for various areas and wiring methods. Do these apply to data cables (ex. cat. 6 or coax) or just mains wiring?
NEC 800.47 would be the governing section of Code for this situation, but it is mum on the topic of burial depths for underground communications cables. In addition, neither 800.3 nor 800.24 references 300.5, so it can't apply that way either.
After remembering I had a contact in my local permitting office, I called and found that (in my jurisdiction, at least) data cables are not regulated.