Papyrus Riddle: Ray of Hope
Find the riddle in the Tomb of Alexander, in the city of Alexandria.
"In the Qatara (sic) Depression there is only one place that isn't dry and sad. At dawn's first light, there one there near the valley's entrance whose roots are halfway between Ra's glory and Apophi's (sic) shadow. Find me there, but make hast, for Ra moves quickly."
The valley in question is the one with the Aquifer Oasis.
The tree closest to the entrance (ie, farthest from the oasis) is the one in question- loot it for the treasure. (note that using Dusk & Dawn sets the a shadows a bit past what the riddle requires).