Seventeen-year-old Ben Story said he and his family were asleep in their Larkspur home, 30 miles south of Denver, when the bear managed to open the unlocked door of his 2008 Toyota Corolla early Friday and climbed inside.
A peanut butter sandwich left on the back seat is probably what attracted the bear, Story said.
It's not unusual for bears to open unlocked doors to cars and houses in search of food, said Tyler Baskfield, a spokesman for the Colorado Division of Wildlife.
"It happens all the time," he said. "They're very smart."
Once inside, the bear must have knocked the shifter on the automatic transmission into neutral, sending the car rolling backward down the inclined driveway and into the thicket, Story said.
The door probably slammed shut when the car jolted to a stop, he said, trapping the bear inside.
Neighbors had called 911, and deputies freed the bear by opening the door with a rope from a distance. It then ran into the woods.
Story said he'll need a new car because the bear trashed the interior while apparently trying to find a way out.
The bear also left what Story called "a present" on the driver's seat.
"A nice pile, actually," added his dad, Ralph. "Something to remember."
Baskfield said such incidents are worrisome because they endanger the bear as well as the public. Wildlife managers trap and kill problem bears that learn to scavenge for human food and garbage.
"Food was left in the car. It's troubling for us," he said.