The single most important thing in the desert of forever. The life force of the entire region. The cactus patches provide food and water for the whole desert. But it is up to the deserts denizens to follow them. The cacti move to where the water is. When one area of the desert runs dry the cacti disengage their roots from the sand and use them to walk to the nearest water source. Once they arrive at the water supply they redeploy their roots, access the water and so on the process goes. There are many cactus patches and when they move desert caravans form behind them as the life force of the desert are followed by those who call the desert home. Alternatively you could remain where you are. A cactus patch will inevitably walk past you at some point.
Travelers are often less fortunate. Without knowledge of cacti migration they often never see them and succumb to the desert, entering into sandy graves.