Lay and Compact Gravel Base

in my situation 14 just will do it now can't emphasize the importance of setting down a good foundation you want to lay down about four inches of road gravel mix make sure it has good solid rocks in there that will act as both strength but more than that as a water drainage system so when the ice or the snow melts or the rain accumulates or the sprinklers you can get in there the retaining wall won't be lifted up and moved out of place or even get wavy on you once everything is in place go over it with a tamper tamp everything down I believe this one's a nine inch that I got from a local home depot for the next