Mountain Men/Harvest Project

The Harvest takes place in the Harvest Room, where the Grounders are drained of their blood in order for the Mountain Men to survive radiation exposure and to heal their wounds. It is eventually learned that the Mountain Men can survive outside of the mountain only if they use the bone marrow from the Sky People (the 48 in this case).

History
The Harvest Project started when the Mountain Men realized the Grounders adapted to the outside radiation, making them immune to it. Mountain Men were not able to adapt to the outside as they had remained in the Mountain the entire time. This made them realized the grounders blood was required in order to allow their people to finally enter the outside world. The grounders however were presumably not willing to give up their blood to them so Mountain Men would take them by force. To make things easier, through the Cerberus Project, they turned grounders into vicious monsters called "Reapers" in order reap them into the Mount Weather Mines where the Mountain Men inject a drug into the reapers in exchange for grounders.

Victims
Blood Harvest treatment has taken the lives of countless grounders. Bone Marrow Harvest killed three delinquents including Fox. Known victims of the Harvest are:
 * Anya (Survived but killed later on)
 * Echo (Survived)
 * Harper (Bone Marrow - Survived)
 * Monty (Survived)
 * Bellamy (Survived)
 * Fox (Bone Marrow - Deceased)
 * Three unnamed Delinquents (Bone Marrow- Deceased)
 * Raven (Bone Marrow - Survived)
 * Abby (Bone Marrow - Survived)
 * Countless unnamed Grounders (Blood - Deceased/Unknown)

Notes And Trivia

 * It is unknown how the Mountain Men acquired their first group of grounders, but a tactic similar to what they used on the delinquents in We Are Grounders (Part 2) was likely used.