Our house is on a hill and lots of retaining walls. There is a timber wall that butts up against a more decorative, terraced rock retaining wall near the front of the house. Where the two meet there are pretty sizeable gaps where water and dirt (mud) weep out during the winter. What should I pack in these voids to keep the dirt behind the walls where it belongs? Gravel? Cement?
Close up of where timber meets rock: https://imgur.com/oKKmEba
A few steps back: https://imgur.com/reBbLGK