Much of the piping that carries drinking water in the country dates to the first half of the 20th century, with some installed before Theodore Roosevelt was in the White House.
Well, given the state's water situation overall, the old, decaying pipes probably won't be an issue for much longer anyway, after all the water dries up & there's nothing left for them to transport or leak.
'Old' is an over used term. Something has to physically affect the pipe like that. Probably all the earth quakes which started micro cracks that eventually got larger and compromised that section of pipe. The pipe could've even been dinged a couple years ago for landscaping or other utility work let alone earthquakes. I've seen exposed old infrastructure on the street and in a house. Undisturbed it will last.