Caitlyn Jenner is stepping in as a rock for her longtime friend Sophia Hutchins‘ grieving mom Amy, who’s just buried her daughter after her tragic loss, TMZ has learned.

In docs obtained by TMZ, the cause of Sophia’s death has been deferred … but her final resting place is at Holy Cross Catholic Cemetery in Culver City, L.A.

We’re told Caitlyn, knowing Amy lives out of town, offered her a place to stay while they navigate the aftermath of Sophia’s death. Both devastated, Caitlyn and Amy have been leaning on each other for support during this incredibly difficult time.

As we told you, Sophia was riding on her ATV along Caitlyn’s street when she collided with the bumper of a moving car … launching her 350 feet into a ravine.

Our sources tell us responders pronounced Sophia dead at the scene — and have been investigating speeding as a possible factor for the crash.