Ruppelt's account:

A string of UFO sightings in Pueblo, Colorado, hit the front pages of newspapers across the United States. Starting on the night of May 5th, for six nights, the citizens of Pueblo, including the Ground Observer Corps, saw UFO's zip over their community. As usual there were various descriptions but everyone agreed "they'd never seen anything like it before."

On the sixth night, the Air Force sent in an investigator and he saw them. Between the hours of 9:00P.M. and midnight he saw six groups of triangular shaped objects that glowed "with a dull fluorescence, faint but bright enough to see." They passed from horizon to horizon in six seconds.

The next day this investigator was called back to Colorado Springs, his base, and a fresh team was sent to Pueblo.

Google map of this location.