Gunnison, Colorado was a town settled in an area of virgin forest in Colorado in the 1950s after coal was discovered in the area.
After coal was discovered in an area of virgin forest in Colorado, the town of Gunnison was settled to mine the coal in the 1950s. The town would eventually become known as a place where people would come and go all the time, leaving to seek better lives elsewhere.
Unknown to the residents, a pack of Bisaan existed in the woods around the town. After the town's settlement, the Bisaan began a 27-year cycle where they would abduct townspeople, use them to mate and then die off with their vessels, leaving the townspeople to never see their loved ones again. Most people wrote these cycles of disappearances off as their loved ones simply leaving to find better lives elsewhere as many townspeople tended to do. The first cycle in 1962 took eight people. Due to the orgies the Bisaan took part in while possessing townspeople, some of the town's older folk came to know the cycle as "the chitters" due to the sound of the Bisaan mating call.
In 1989, a second cycle began that took a dozen people. Amongst these people was Sheriff Joe Cochran's daughter. Cochran was able to locate the Bisaan burrow in the old Donnelly mine, but most of the Bisaan had already died off and Cochran was forced to kill his daughter in self-defense. As a result, Cochran stopped his investigation and let people think their loved ones had just run off. He retired as sheriff a few months after the Bisaan cycle.
Amongst the other victims was sixteen year old Matty Cuevas whose disappearance and subsequent mutation into a Bisaan was witnessed by his younger brother, Jesse. No one believed Jesse's story with Cochran refusing to back him up. Jesse eventually left town and became a hunter, intending to return to Gunnison for the third cycle and to put an end to the Bisaan to get his revenge.
In 2016, the third Bisaan cycle in Gunnison began and drew the attention of hunters Sam and Dean Winchester. The Winchesters teamed up with Jesse and his husband Cesar to stop the Bisaan. Dean and Cesar eventually tracked down the Bisaan burrow and killed all of the monsters, ending their attacks on Gunnison for good. In the burrow, the hunters found the bodies of all of the Gunnison residents killed by the Bisaan and the Winchesters burned the remains to properly put them to rest.