From memory, the airfield (first used in the 1920s, apparently) was
sold (or returned to) a local landowner in the late 50s (not the
70s). It is now the site of a small industrial estate. No
aircraft had been based there for years beforehand - probably since
shortly after WW2. It was known as Royal Naval Air Station (RNAS)
Newton and was within sight of the British Royal Navy base at
Invergordon.

As you say, US personnel were present in the mid-50s (and possibly
earlier) and launched balloons but I understood these to be weather
balloons. What makes you think they were spy balloons?

The final Royal Navy personnel left around 1961.

Thank you for the information.

The "weather balloon" story was a cover up for the real fact: overfly
of the Soviet Union using high tech imaging gear attached to them. The
project code named "genetrix" was a disaster, because the soviets
shoot down a lot of balloons and the only few wich crossed away and
reached the Pacific Ocean obtained no much value information.

More information is available in the book from Curtis Peebles "The
Moby Dick Project: Reconnaissance Balloons Over Russia" and a nice
article on the subject you will find in
http://worldatwar.net/chandelle/v4/v4n1-2/balloons.html

Greetings

LEP