The couple split in June but vowed to put their children first and continue to spend time together as a family, reported People magazine.
According to a source the former couple and parents to Violet, 10, Seraphina, 6 and Samuel 3, are spending time in the Big Sky state.
"(Garner) wants to get along with Ben for the kids' sakes," the source said
Affleck and Garner, both 43, have tried their best to put their differences aside and do what is best for the children.