Due to the hilly terrain of the zoo's riverside location, grades of up to 6% (for most railroads 2% is considered steep) were required and some of the curves were well under 150 feet (46 m) in radius.

Passengers boarded at the "Omaha Depot" located in the Aksarben Nature Kingdom (today known as Glacier Bay Landing) and rode to "Promontory Junction" at the south end of the zoo's lagoon.

119 (the famous locomotive used in the laying of the real "golden spike" marking the transcontinental line's completion), and the four coaches were given names significant to the UP's history.

UP's influence was perhaps most evident in the Omaha Zoo Railroad's logo: a Union Pacific shield with the Esso tiger superimposed.

Though the direct references to Union Pacific place names have faded over the years, UP's support of the zoo's railroad has remained strong.

By chance, a small tank locomotive of Austrian Heritage named "Riva" was found in Romania, and its owner Plasser & Theurer was willing to donate it to the zoo.

In the early years, the train commonly ran figure eights through the zoo using the connecting track and often reversed direction on the wyes.

This practice ended in the early 1970s due to the need for faster turnarounds and Riva's inability to negotiate a tight curve on the north (Bailey) wye.

Today, the trains circle the park clockwise, covering roughly 1.8 miles (2.9 km) and taking 15–20 minutes on each circuit.

Originally painted black and red, it emerged resplendent in a beautiful maroon and blue scheme and featured a new wooden cab.

In 2022, the cab received a small placard honoring the late Henry Morris Jr. who served the railroad for 36 years.

Generating a tractive effort of 10,600 pounds, it has almost twice the pulling power of 119 and typically operates with a train consisting of six open-air coaches + a caboose.

Riva began its long career in 1890 when it was turned out by the Krauss Works of Linz, Austria as serial number 2360.

World War II brought another stint in military duty before the engine finally ended up on the State Railways of Romania (CFR) as number 395–104.

"Riva" operated on the CFR's Alba Julia–Zlatna line until 1968, when it was finally retired and sold to Plasser & Theurer, an Austria-based builder of track maintenance machinery.

The overhaul consisted of major running gear work, American air brake equipment installation, and conversion from coal to oil fuel.

The reborn "Riva" entered service at the zoo in 1976 during the annual Family Night/Members' Day event, and has operated almost every year since.

When the engine arrived at the zoo in 2008, it was painted light blue and featured a likeness of a woman's face (presumably that of its previous owner's wife).