RED GLOWING SPHERE FLIES NEAR GROUND IN ARIZONA DESERT

A friend + I were camping at night in the in Arizona desert mountains outside Phoenix. My friend worked for an airline at Sky Harbor Airport + I was a secretary.  He got off work at 11pm and we arrived at camping location by 11:45pm.  It was a clear desert night with no clouds, far from the city lights.
 We camped by our truck which was down a dirt road near the entrance to a long canyon with tall rocky walls.  We had just been there for a short time when a far off red dot of light at the far end of the canyon caught our attention. It was slowly coming towards us.  It was a red glowing sphere or orb that was approximately 3 feet wide.  This sphere flew steadily towards us at approximately walking speed, about 8 feet above the ground.
 The sphere traveled along the canyon wall always staying exactly the same distance from the wall's  surface, as if mapping exactly all the rocky outcroppings and terrain variations.  It made absolutely no sound at all.
 As it approached us, we froze, grabbing each other's arms + staying silent.  It flew directly by us, only about 12 feet away.  We could see the steady red glow of the orb's "light" reflecting off the canyon wall, illuminating it clearly, as it flew slowly by us.  We stood still and watched it for another minute as it traveled on past us and down into the long canyon until it disappeared from view.