The Spaceport

Phoenix Trotting Park in Goodyear, Arizona.
A failed horse harness racing track venture. It was built in 1964 at a cost of 10 million dollars (7 million over budget) and opened in 1965.
It stood empty since it's closing in December of 1966.
Unfortunately in September and October of 2017 it was demolished. It's a shame that a practical use couldn't be found for for this interesting structure.