We chased Giant Gray Cubes through the desert near Tucson, AZ.

Looking northwest from downtown Tucson I saw two dark gray cubes, roughly the size of  small houses, at a height of approx. 400 feet, in loose formation, traveling horizontally toward the west northwest. My female friend  and I (male)(we were both students at the Univ. of Arizona at the time, living off campus), hopped on my motorcycle, a 1985 Honda 500cc Interceptor, and began pursuit, heading toward Phoenix on Interstate 10. I was riding in excess of 90 mph. They were out of site for several minutes, but became visible again once we cleared some hills south of Marana, AZ.
They were 2 or three miles away toward the west..we took an offramp..Tangerine Rd..maybe..and continued high speed pursuit. They had decreased their altitude to about 100 feet above ground..i got within a quarter mile..they were dark gray..matte finish..no visible protrusions, holes, or lights..just plain gray cubes...traveling together..but moving independently,,bobbing up and down. They increased their speed to match ours apparently..never letting us get closer than about 1/4 mile. They settled over a rise in the road..and in the 12 to 15 seconds it took us to reach the rise they were no where in sight. I reported it to David Monthan AFB...after playing phone tag for 30 minutes,,mostly on hold, they told me that the giant cubes we saw were marker ribbons dropped by the Air Force.