IIRC, that C-4 went adrift after an "extended exercise" by Marines around 29 Palms. Haven't been a dirt Marine but can certainly see where ten pounds of something could go missing, especially if the dude(s) packing it around along with those 50 pound rucks were to be (for example) awakened and sent hurtling into the night by some irate Gunny.
I have personal knowledge of a report involving a complete jet aircraft that (briefly) turned up AWOL long, long ago, but of such stuff is the life and bane of the Supply Corps.
I'll cheerfully bet a six-pack that the C-4 is even now sitting in the hole out in the desert where it was accidentally left.
You will I hope pardon me for chuckling a bit about this because the bidendecree shutting down the Keystone has just about nuked the Eastern third of Montana, including a whole lot of friends and family which has me just about to go to war and I need some comic relief right now.
I remember when a certain amount of that was used by the cia on loudoun County school buses for police/school/dog training and was accidently left on the bus. A bus driver found it, it was attached under the bus.
Thanks for insight about missing C-4. If Trump and plan does not work, I see no alternative but something extremely Not Nice.