So the fires in Texas came dangeroulsy close to my bug out location.  Most of our prep items
are above ground.  

My question is this.  How deep would you have to bury weapons and ammo to keep it safe from fire?

We moved most of it to the center of a pasture, more to protect the fireman than the gear itself.

only a couple of inches.  The dirt is a fantastic insulator.

you're going to have to go deeper than a couple inches.  If it's not in an enclosed space, i.e well protected basement or well protected underground storage unit then you need to get under the root systems.  They have been known to burn for months and years.  Wildfires don't just burn above ground, they burn below in the root systems as well.

Your best bet is to get a fire rated box and either bury that or put a fire rated box in your basement