I was up on the roof and looked down to see the contractors mixing concrete for the meteorological tower base. At the "top" of the picture, you see empty bags of cement. Below that, the yellow cement mixer. They would throw a half-bag of cement in the mixer, five gallons of water, and --- see that pile between the truck and the mixer? That's decomposed granite. It's a kind of a coarse sand if you aren't familiar with it -- then they'd throw in 50 shovels of sand. They called it concrete, but I know better. They'd pour it into a five-gallon bucket and dump it into the back of the pickup. The mixture was so wet it would splash when they poured it in.
After an hour of mixing this "concrete" up, they'd have the pickup full, drive out to the tower, and scoop it out five gallons at a time.
When we asked them about gravel, they said you can't get it. When I looked around at other construction sites, I believed them. I saw one pile (about four cubic yards) of gravel the whole time I was there.