Oh! look at that --- the USA has a 'Mach Loop'
Yeah,
Rainbow Canyon aka
Star Wars Canyon in Death Valley, it's been used for high-speed
flight training and aircraft testing since WWII.
Edwards AFB, Nellis AFB, NAS LeMoore, MCAS Miramar, Fresno ANG, Plant 42 (Palmdale), and various
testing outfits use it today.