I spotted this helium-filled "mini blimp", which is 233 ft. long and made of multi-layered kevlar, while driving down to Palomas, Mexico. It can reach 15,000 ft. altitude and provides surveillance of an area 300 miles in diameter.
There are 6 aerostats and they all send their data to the Federal Command, Control and Communications and Intelligence Centers in Riverside, CA. Installed in March 1991 and operated by the U.S. Air Force they provide vital information to the U.S. Customs and Drug Enforecement Agency.
Why are these blimps tethered so high in the sky? To capture information about aircraft crossing the border that attempt to "fly under the radar" and avoid detection. These "eyes in the sky" will catch 'em. They hope.

According to the staff at Pancho Villa State Park, we have 6 of these and the other locations are: Yuma and Tucson, AZ; Marfa, Eagle Pass, and Rio Grande City, TX, and one more that is 40 miles into the Gulf of Mexico .