There are sites all around Yaoundé where we can see people burning large boulders to weaken them enough to break them off and start chiseling it into gravel.  Hard work!  It reminds me of the cartoon the Flintstones.  I remember as a little girl being excited to ride in the ton truck to the rock quarry to get gravel for building projects or driveways.  I remember machines doing all the breaking.  I can’t imagine how labor intensive it would be to make gravel by hand.  You can purchase the gravel packaged in burlap type sacks on the side of the road by the work sites.