Strange "blimp-like" object seen hovering over desert where military practice.

I was onboard a commercial flight from San Diego to Newark on July 7, 2021.  We flew east from San Diego along the US/Mexico border.  I was on the left side of the plane so I could see the US side of the border.  I knew from monitoring FlightRadar24 that there was an area east of El Centro, CA., where I typically notice military aircraft flying.  So as we were nearing that area, I was looking out the window wondering if I would see any military aircraft.  At about 12:45, I saw a strange silvery-white object hovering over the ground below and to the left of our flight path.  If I had to guess, it appeared to be about 2500 feet AGL and we were at about 20000 feet AGL at that time.  The object appeared to be stationary.  I remember thinking that it exhibited the flight characteristics of a tethered balloon.  I snapped a photo of the object.  I blew the photo up and it almost looks like a short, fat blimp with a weird protrusion on the right rear side.  I am thi! nking that this may be some sort of military craft or drone, but I have no idea.  I assumed that it was stationary since we were moving quite fast and I lost sight of the object as we passed and my view became obstructed by the wing of our aircraft.  I will submit the photo and the blown up version to you via email.