Flight 306 landed in Grand Junction at about 11 a.m. after a warning light indicated smoke in the cargo area and a passenger smelled smoke. All 109 passengers and crew got off the plane safely.
United spokesman Mike Trevino said airport firefighters found no visible smoke anywhere in the plane. No injuries were reported.
A replacement plane arrived to take everyone to Baltimore at about 2 p.m. to take the passengers to Baltimore.
The Associated Press contributed to this story.