This page of the Far Cry 6 guide describes a treasure hunt High Supply available in Madrugada.
District: Palma Forest.
To start the treasure hunt, you must read the note attached to the rock. Then you must head to the mountains - climb, use the rope and vines to get as far as possible.
Eventually you'll spot the supplies you need. To reach them, you must destroy the rocks standing in your way. You can use a launcher to open the way forward with a single rocket. Reaching and taking the supplies completes the mission.