From Halopedia, the Halo wiki
As a part of the Joint Occupation Zone project between the Swords of Sanghelios and the United Nations Space Command, the Sangheili refugees of the colony world of Glyke came to Carrow in order to build a new life. Led by Kaidon Rojka 'Kasaan, these Sangheili settled around the Astlehich River and established a collection of Keeps that became the city of Rak. Later, a group of humans traveled to this spot with the intent of forming a settlement there. Finding the Sangheili already there, these colonists instead established the settlement of Sandholm in the Uldt Desert.
A map of the Uldt Desert containing the location of the Astlehich River