“Flying Saucers Spotted Over Atom Test Site”,
18 April 1952 (Rome News-Tribune, Georgia)
On 17 April 1952, five men at the Nellis U.S. Air Force Base near Las Vegas sighted 18 disk shaped UFOs over a Nevada test site, where important new nuclear tests are being made, the Rome News-Tribune reports:
http://news.google.com/newspapers?id=A4MEAAAAIBAJ&sjid=hDEDAAAAIBAJ&pg=5005,1472222
The Nevada Nuclear Test Site is located 145 kilometres (90 miles) north of Las Vegas.

Aerial view of the Nevada Nuclear Test Site (longtail.com photo)