Big Boy No. 4012 at Steamtown National Historic Site has been pushed to a siding for much-needed restoration/NPS

Thirty years' of weather have taken a toll on Union Pacific "Big Boy" No. 4012, a crowd-drawing steam locomotive at Steamtown National Historic Site that has been pulled to a siding for some much need cosmetic restoration work.

"There’s some metal work that needs to be taken care of, sitting outside for the past 30 years," said Bill Fischer, Steamtown's chief of visitor services and resource management, during a phone call Wednesday. "There’s some rust that needs to be taken care of.”

No. 4012 is the only one of its type located east of the Mississippi River, and is a popular attraction. This has been especially true this year because of the Union Pacific Railroad’s restoration of sibling “Big Boy” No. 4014 to full operational capacity. That locomotive, which is based in Cheyenne, Wyoming, was an important component in commemorating the 150th anniversary of the completion of the first Transcontinental Railroad, which the Union Pacific helped construct between 1863 and 1869. No. 4014 went back on the tracks this past summer, chugging and smoking from Cheyenne to Ogden, Utah, to celebrate the anniversary.

During their heyday, the “Big Boy” locomotives were critical contributors on the Home Front during World War 2 moving heavy freight and war materiel.

Steamtown National Historic Site, located in Scranton, Pennsylvania, will provide occasional updates on the park’s website and social media on the status of “Big Boy” No. 4012’s cosmetic restoration and painting.

"While we realize that many visitors come specifically to Steamtown NHS to view this leviathan of the rails, and will be disappointed that it is not on display, the end result shall ensure that future visitors will be even more impressed with their views of what is one of the largest steam locomotives ever built," park staff said.

Located in downtown Scranton, Pa., Steamtown is open daily from 9 a.m. – 5 p.m.