From the zoo's web site:
Originally Posted by Wotan
This diesel-powered streamliner was built in 1958. A replica of General Motors’ "Aerotrain," the engine’s 165 horsepower is transmitted to eight driving wheels through a hydraulic-type torque converter transmission and spiral gears. Safety features include a "dead man control" to ease the train to a halt in an emergency. A governor holds the train to a 12-mile-per-hour maximum. A conventional automatic air brake system provides safe train handling.
From the Wikipedia Aerotrain page, about the Viewliner:
On June 26, 1957, the narrow-gauge Santa Fe and Disneyland Viewliner (billed by Disneyland as "the fastest miniature train in the world") commenced operation. Two separate trains, designed and built as scale replicas of the futuristic Aerotrain, traveled along a figure-eight track through parts of Tomorrowland and Fantasyland parallel to a portion of the DLRR main line. The Tomorrowland train featured cars that were named for the planets, while the cars of the Fantasyland train were named after various Disney characters.
The modern, streamlined trains were placed into service to represent the future of rail travel, in contrast to the steam-powered DLRR which represented its past. Motive power for each train consisted of an integral head-end unit driven by an Oldsmobile "Rocket" V8 gasoline engine. Oldsmobile also furnished the windscreen, doors and instrument console for each of the two 5,000 lb (2,300 kg) locomotives. The attraction operated until September 15, 1958, when construction began on the Matterhorn and Submarine Voyage; the Disneyland Monorail System ultimately took the place of the Viewliner in June of the following year.
The two trains look similar in the photos on the web pages, but they're not quite identical.