How did six feet become the standard burial depth?
-- LB, Poway
Was it ever? Don't think so. S'mattera fact, there's no law in California or in most other states that says a grave has to be dug to a certain depth. California's Health and Safety Code requires that when the grave is filled in and brought up to ground level, there's at least 18 inches of dirt and turf over the top of the vault or casket. Most graves these days are dug with backhoes and can vary between four and five feet deep. Maybe eight or nine if the site will eventually hold two stacked coffins.
If you like gory reading, forget about Stephen King. Try a history of the mortuary industry. Until sometime in the 1800s, before the advent of metal coffins and burial vaults, bodies were sometimes haphazardly buried in shallow graves, since it was up to the families to dig them. After a few years, once the wood coffin and flesh started rotting, the gravesite would sink, and skulls and bones sometimes made unscheduled appearances. This is especially true in cold climates, where frozen ground expands and can cause unsightly upheavals. These same mortuary historians speculate that six feet might have been the depth that was considered safest if you didn't want your loved one popping up again at some future date.