From Halopedia, the Halo wiki
Sandholm is situated under a rocky bluff on the banks of a dried riverbed. It is situated on a north-easterly axis and contains the main street, which is made of hard-caked mud and has a total of twenty houses lining it. Each house contains two bedrooms, a bathroom, a kitchen, and a heavy door and window shutters that are designed to withstand severe sandstorms. These residentials also each contain a M295 DMR for defensive purposes, contained in a footlocker near the door. There is additionally a doctor's shed which, at one point, contained a Mongoose. Signal Hill is located just outside of Sandholm and is where the settlement's radio receiver was set up before it was destroyed.
After the conclusion of the Human-Covenant War, a group of human refugees traveled to Carrow with the intent of creating a settlement on the banks of the Astlehich River. Discovering that this land had already been settled by the Sangheili who had founded the city of Rak, the human colonists traveled south into the Uldt and created Sandholm. There they attempted to carve out an existence by drilling for water and trading with travelers in the desert.
In July of 2558, a Viral hemorrhagic fever swept through Sandholm and decimated the population, killing many and leaving the survivors in an extremely weakened state. A series of severe sandstorms also destroyed the communications repeater, cutting the settlement off from the rest of the planet. With medical supplies dwindling and the situation looking grim, a girl named Dalhia left Sandholm in order to try and find help at Masov Oasis to the northwest. She succeeded, and soon the Surakan Militia Volunteers descended on Sandholm to provide medical assistance to the survivors.