There appears to be a large-scale military exercise underway across Nevada and Utah. In the dead of night, a variety of U.S. surveillance and support aircraft have popped up over and around Las Vegas and Dugway Proving Ground west of Salt Lake City. The most interesting of the lot is a U-2 Dragon Lady serial number 68-10366, which is based out of Plant 42 in Palmdale, California and is normally used to test new U-2 payloads and configurations. The U-2 has been flying long tracks that cross over South Las Vegas for hours at an altitude of 60,000 feet. This is not a common flight profile for any U-2.

https://www.thedrive.com/the-war-zone/27339/a-u-2-spy-plane-is-flying-tracks-high-over-south-las-vegas