Actually, all of the Corkscrew is considered to be "Lower Antelope Canyon" instead of Upper Antelope as implied here. Calling it upper can be quite confusing since the Navajos, all guidebooks, and there permit consider it to be lower Antelope. Corkscrew and all the canyon below the highway is Lower Antelope. The Crack and Canyon X are in Upper Antelope.
Perhaps clarify this by refering to it as Upper Corkscrew rather than "upper canyon" to avoid some confusion.
The below is just my opinion:
Pehaps chance this to "a jewel" instead of "the jewel" beause there are actually better slot canyons out there. Just my opinion about changing the above though.