Gamma Forests

The Gamma Forest was an unknown location. The girls from there were sometimes known as "Gamma Girls". It was "Heaven-neutral", referring to its neutral stance towards recruitment for the Church. The people there were known to craft handstitched cloth symbols of devotion called "prayer leaves". These were embroidered with the names of one's children in the native tongue of the people of the Gamma Forests, as a sign of belief that child would always come home to them.

The first reference to the forests was by Idris as she was dying. She repeatedly told Rory Williams that "the only water in the forest is the river", leaving him confusion. Rory recounted the statement to the Doctor. (DW: The Doctor's Wife) This was later discovered to reference that in the Gamma Forest tongue, the only word for "water" translates to "river". (DW: A Good Man Goes to War)

When Lorna Bucket was a child, she met the Doctor there. She recalled that he repeatedly told her to "run". She also claimed that the reason she enlisted was partly because the Doctor's short visit to the forests was the only thing that had ever happened there. Lorna later crafted and gifted a prayer-leaf to Amy Pond, who had recently been separated from her newborn daughter.

Later as Lorna died, the Doctor pretended to recall their adventure there, despite the fact he had not yet met Lorna in his own timeline. After Lorna's death, River Song appeared and mentioned the Gamma Forest in part of her argument that some of the horrors he faced now was a result of what he had become, and mentioned that the people of the Gamma Forests define "doctor" as "mighty warrior".

After the Doctor left, Amy Pond and Rory confronted River, who prompted them to look at the prayer leaf, explaining the name was translated this way because "...the only water in the forest is the river." The letters translated the forest's words for "pond" to "river", and "melody" to "song". (DW: A Good Man Goes to War)