Union Pacific No. 3985 or UP No. 3985 is a 4-6-6-4 Challenger type steam locomotive owned by the Union Pacific Railroad. 3985 was built in 1943 by the American Locomotive Company of Schenectady, New York. The locomotive is one of only two of the original 105 Union Pacific Challengers in existence, the other being Union Pacific No. 3977 on static display in North Platte, Nebraska.
3985 is currently in the UP roundhouse shops in Cheyenne, Wyoming and is undergoing boiler work and overhaul since 2010. Her restoration may resume after Big Boy #4014's restoration is complete.