TMGT
Elite Member
It's hard to tell with the washed out pic and I'm in my phone, but almost looks like rubber mulch.This looks too smooth for gravel and is more humped in the middle than you would expect gravel too be. Tires also would sag more if indeed 4 tons of gravel. I'm going with something like mulch or some recycled material but it's just a hunch.
The tires appear to be P metric, if so there's no way there is more then 1.5-2 tons in that thing.