They also attempted to use a gravitational system to slowly lower the ride, but it was unsuccessful.
Fire crews were then forced to use a rope system and lower each passenger one-by-one.
There were no injuries reported, fire officials said.
"What we're gonna do right now is formulate a plan on exactly how to bring them down," Capt. Larry Kurtz earlier told CBS2.
All 20 passengers and one ride operator were brought to the ground safely shortly before 10pm local time, according to Knott's Berry Farm representatives.
In a statement, theme park officials said rides are always checked.
"Each of Knott's rides is inspected, check-listed and properly maintained daily. Sky Cabin will remain closed until the park's investigation into the cause of the incident is completed," it said.
It was not immediately clear what may have caused the ride to stall.
Knott's Berry Farm describes the Sky Cabin as a "fully enclosed revolving observation ride."