Above ground "High Temperature, Low Sag" cables can reach 200°C. Underground cables can still go up to 90°C, which is still flamin' hot. They're usually buried at least 1 meter deep, which gives the heat a decent chance to dissipate. But in those areas with high chances of fires, I'd be wary all the same :-/.
Of course, the above mostly applies to high voltage & high current situations, think 150kV, 300MVA monster connections. I doubt PG&E manages 10k miles of high voltage power lines. If we're talking residential interconnections, there won't be any issues burying those.
I would have thought they'd need to put sections of cooling in, if not maybe they have some form of oil or other liquid to help dissipate the heat? I thought one of the many reasons why the UK still does overhead between chunks of the grid is for cooling and easier maintenance.
Of course, the above mostly applies to high voltage & high current situations, think 150kV, 300MVA monster connections. I doubt PG&E manages 10k miles of high voltage power lines. If we're talking residential interconnections, there won't be any issues burying those.