Stable 90 was one of the Stables built by Stable-Tec in the Hoofington Region of Equestria, set up with all of the advanced gear and amenities that were needed to have its inhabitants survive the coming apocalypse by the Zebras. However due to events completely unknown to Stable-Tec and the replacement Overmare Buttercup; the Stable was stripped of all its components, leaving behind only the Overmares' office, walls, ceiling, floor, metal walkways, and the massive gear-shaped door and accompanying exterior door mechanism. The Stable Dwellers that went into the Stable on The Last Day, were shocked to find out that it was just an empty hole in the ground, and 12 days after entering, the Stable Dwellers had finally exhausted the supply of food that they brought in with them, and began to feed upon the dead corpses, possibly succumbing to the effects of the Raiders Disease until the only one left was the Overmare 10 days later, 24 days after entering the Stable Buttercup concluded with Stable 90 being the 'shortest-lived Stable in Equestria' who chronicled the history of their stay in Stable 90 on old candy wrappers since there were no terminals, air filters or water talismans inside.
Two centuries later, Stable 90 became a small safe haven for Blackjack and Morning Glory, after fleeing from Zodiac Leo and his band of mercenary hunters, staying inside of the Stable, Blackjack began having her first hallucination encounter with the Dealer.
Later after Blackjack killed off the Raider Diseased-inhabitants within Stable 99, she left for Star Point to commit suicide for her actions and all the ponies she killed or allowed to die on her watch. She discovered the bones of a mare, along with recordings, downloading the recordings she discovered that her ancestor Tarot and her surrogate mother Marigold were originally slated for Stable 90 but were too far away from it on the Last Day and instead made it for Stable 99, Tarot and Marigold weren't allowed entry, but Card Trick: the mare who would become the first chief of Security in Stable 99, who stated that anypony admitted to a Stable was allowed to bring in one child -regardless of which Stable they were set for in the first place- and Tarot was allowed in.
It was later found out that the Gardens of Equestria project was actually built by Goldenblood using components he stole from Stable 90 and erased the memories of those involved in the 2 year construction.