This TNT miniseries focused on the westward expansion in the 19th century, so of course railroads were featured. 

The fourth episode, "Hell on Wheels" focuses on the Transcontinental Railroad and features work trains of the Central Pacific and Union Pacific. It is often difficult to pinpoint exactly which locomotives are used where but the Virginia & Truckee's #21 "J.W. Bowker" was used as well as Black Hills Central #7; a Prairie-type from 1919. The Bowker is one of 2 surviving Baldwin 2-4-0's in existence, and currently is on loan to the Nevada State RR Museum in Carson City. The #7 was active pulling tourist trains on the Black Hills Central but now resides on static display outside their Hill City depot in South Dakota. 

Next we see a true American-type arriving on the scene, the famous Virginia & Truckee #11 "Reno" representing the Union Pacific #119. The Reno today resides at the NSRM as well, and is under restoration.

For the fateful meeting at Promontory Point, the Reno is joined by the Bowker, which is dressed up to represent Central Pacific's #60 "Jupiter." On a side note, both of the real engines present at the Golden Spike Ceremony were sold for scrap in the early 1900s. However, faithful reproductions have been produced that re-enact the event at the site where it occurred (now a National Park). Above you can see both engines reunited once again at NSRM at the "Great Western Steam Up" in 2020. 

Later in episode 5, "Casualties of War" we catch a brief glimpse of Black Hills Central #7 again in the background painted up as a Union Pacific #7. Above is a picture of it in Hill City in 2020.