The Sky Riders appeared in Wonder Woman no.23 in 1947. The story was republished in 1974 with different artwork. The Sky Riders were a group of alien women who invaded Paradise Island during Wonder Woman's childhood and tried to enslave the Amazons. They wore bestial masks and rode on flying mammals called Kangas.
The Amazons believed that the Sky Riders were male and that the presence of men on Paradise Island had broken their power. However, the young Princess Diana unmasks one of the Sky Riders revealing them to be women. They are overpowered by the Amazons, stripped of their protective suits and are taken prisoner.
The Sky Riders' leader asks if they can be allowed to join the Amazons. Queen Hippolyta did not trust them, however, and had them sent to the Amazon prison on Transformation Island, to be taught the Amazon discipline of obedience to loving authority. They are led away in their underwear.
As we don't hear about them again, it may be that they were reformed and joined the Amazons. On the other hand, we see a lot of unnamed inmates on Transformation Island in other stories. These may be Sky Riders.
The story explains the origin of the Kangas that Amazons ride.
The Sky Riders were one of a number of Golden Age Wonder Woman villainesses who disguised themselves as men- Doctor Poison, Hypnota, King Neptune and Blue Snowman.